FYI, a refresh of the task editor fixes this problem if you see it, but a fix is in the works.

java.lang.NullPointerException
at org.eclipse.mylyn.internal.tasks.ui.editors.AttachmentTableLabelProvider.getAttachmentId(AttachmentTableLabelProvider.java:133)
at org.eclipse.mylyn.internal.tasks.ui.editors.AttachmentTableLabelProvider.getColumnText(AttachmentTableLabelProvider.java:126)
at org.eclipse.mylyn.internal.tasks.ui.editors.AttachmentTableLabelProvider.update(AttachmentTableLabelProvider.java:210)
at org.eclipse.jface.viewers.ViewerColumn.refresh(ViewerColumn.java:152)
at org.eclipse.jface.viewers.AbstractTableViewer.doUpdateItem(AbstractTableViewer.java:399)
at org.eclipse.jface.viewers.StructuredViewer$UpdateItemSafeRunnable.run(StructuredViewer.java:481)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.ui.internal.JFaceUtil$1.run(JFaceUtil.java:49)
at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:175)
at org.eclipse.jface.viewers.StructuredViewer.updateItem(StructuredViewer.java:2141)
at org.eclipse.jface.viewers.AbstractTableViewer.internalRefreshAll(AbstractTableViewer.java:711)
at org.eclipse.jface.viewers.AbstractTableViewer.internalRefresh(AbstractTableViewer.java:649)
at org.eclipse.jface.viewers.AbstractTableViewer.internalRefresh(AbstractTableViewer.java:636)
at org.eclipse.jface.viewers.StructuredViewer$7.run(StructuredViewer.java:1487)
at org.eclipse.jface.viewers.StructuredViewer.preservingSelection(StructuredViewer.java:1422)
at org.eclipse.jface.viewers.StructuredViewer.preservingSelection(StructuredViewer.java:1383)
at org.eclipse.jface.viewers.StructuredViewer.refresh(StructuredViewer.java:1485)
at org.eclipse.jface.viewers.ColumnViewer.refresh(ColumnViewer.java:537)
at org.eclipse.jface.viewers.StructuredViewer.refresh(StructuredViewer.java:1444)
at org.eclipse.mylyn.internal.provisional.commons.ui.TableViewerSupport.restore(TableViewerSupport.java:143)
at org.eclipse.mylyn.internal.provisional.commons.ui.TableViewerSupport.<init>(TableViewerSupport.java:66)
at org.eclipse.mylyn.internal.tasks.ui.editors.TaskEditorAttachmentPart.createAttachmentTable(TaskEditorAttachmentPart.java:183)
at org.eclipse.mylyn.internal.tasks.ui.editors.TaskEditorAttachmentPart.expandSection(TaskEditorAttachmentPart.java:249)
at org.eclipse.mylyn.internal.tasks.ui.editors.TaskEditorAttachmentPart.createControl(TaskEditorAttachmentPart.java:226)
at org.eclipse.mylyn.tasks.ui.editors.AbstractTaskEditorPage.initializePart(AbstractTaskEditorPage.java:1290)
at org.eclipse.mylyn.tasks.ui.editors.AbstractTaskEditorPage.access$6(AbstractTaskEditorPage.java:1282)
at org.eclipse.mylyn.tasks.ui.editors.AbstractTaskEditorPage$14.run(AbstractTaskEditorPage.java:867)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.mylyn.tasks.ui.editors.AbstractTaskEditorPage.createParts(AbstractTaskEditorPage.java:858)
at org.eclipse.mylyn.tasks.ui.editors.AbstractTaskEditorPage.createParts(AbstractTaskEditorPage.java:842)
at org.eclipse.mylyn.tasks.ui.editors.AbstractTaskEditorPage.createFormContentInternal(AbstractTaskEditorPage.java:729)
at org.eclipse.mylyn.tasks.ui.editors.AbstractTaskEditorPage.createFormContent(AbstractTaskEditorPage.java:674)
at org.eclipse.ui.forms.editor.FormPage$1.run(FormPage.java:152)
at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
at org.eclipse.ui.forms.editor.FormPage.createPartControl(FormPage.java:150)
at org.eclipse.mylyn.tasks.ui.editors.AbstractTaskEditorPage.createPartControl(AbstractTaskEditorPage.java:632)
at org.eclipse.ui.forms.editor.FormEditor.pageChange(FormEditor.java:471)
at org.eclipse.ui.part.MultiPageEditorPart.setActivePage(MultiPageEditorPart.java:1067)
at org.eclipse.ui.forms.editor.FormEditor.setActivePage(FormEditor.java:603)
at org.eclipse.ui.forms.editor.SharedHeaderFormEditor.setActivePage(SharedHeaderFormEditor.java:110)
at org.eclipse.mylyn.tasks.ui.editors.TaskEditor.addPages(TaskEditor.java:407)
at org.eclipse.ui.forms.editor.FormEditor.createPages(FormEditor.java:138)
at org.eclipse.ui.forms.editor.SharedHeaderFormEditor.createPages(SharedHeaderFormEditor.java:98)
at org.eclipse.ui.part.MultiPageEditorPart.createPartControl(MultiPageEditorPart.java:348)
at org.eclipse.ui.internal.EditorReference.createPartHelper(EditorReference.java:670)
at org.eclipse.ui.internal.EditorReference.createPart(EditorReference.java:465)
at org.eclipse.ui.internal.WorkbenchPartReference.getPart(WorkbenchPartReference.java:595)
at org.eclipse.ui.internal.EditorReference.getEditor(EditorReference.java:289)
at org.eclipse.ui.internal.WorkbenchPage.busyOpenEditorBatched(WorkbenchPage.java:2863)
at org.eclipse.ui.internal.WorkbenchPage.busyOpenEditor(WorkbenchPage.java:2768)
at org.eclipse.ui.internal.WorkbenchPage.access$11(WorkbenchPage.java:2760)
at org.eclipse.ui.internal.WorkbenchPage$10.run(WorkbenchPage.java:2711)
at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java:2707)
at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java:2691)
at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java:2674)
at org.eclipse.mylyn.tasks.ui.TasksUiUtil.openEditor(TasksUiUtil.java:177)
at org.eclipse.mylyn.internal.tasks.ui.util.TasksUiInternal.openTask(TasksUiInternal.java:890)
at org.eclipse.mylyn.tasks.ui.TasksUiUtil.openTask(TasksUiUtil.java:280)
at org.eclipse.mylyn.internal.tasks.ui.util.TasksUiInternal.refreshAndOpenTaskListElement(TasksUiInternal.java:291)
at org.eclipse.mylyn.internal.tasks.ui.actions.OpenTaskListElementAction.runWithEvent(OpenTaskListElementAction.java:56)
at org.eclipse.mylyn.internal.tasks.ui.actions.OpenTaskListElementAction.run(OpenTaskListElementAction.java:47)
at org.eclipse.mylyn.internal.tasks.ui.views.TaskListView$20.open(TaskListView.java:1254)
at org.eclipse.jface.viewers.StructuredViewer$2.run(StructuredViewer.java:845)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.ui.internal.JFaceUtil$1.run(JFaceUtil.java:49)
at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:175)
at org.eclipse.jface.viewers.StructuredViewer.fireOpen(StructuredViewer.java:843)
at org.eclipse.jface.viewers.StructuredViewer.handleOpen(StructuredViewer.java:1131)
at org.eclipse.jface.viewers.StructuredViewer$6.handleOpen(StructuredViewer.java:1235)
at org.eclipse.jface.util.OpenStrategy.fireOpenEvent(OpenStrategy.java:264)
at org.eclipse.jface.util.OpenStrategy.access$2(OpenStrategy.java:258)
at org.eclipse.jface.util.OpenStrategy$1.handleEvent(OpenStrategy.java:298)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1053)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4066)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3657)
at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2629)
at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2593)
at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2427)
at org.eclipse.ui.internal.Workbench$7.run(Workbench.java:670)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:663)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:115)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:369)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:179)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:619)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:574)
at org.eclipse.equinox.launcher.Main.run(Main.java:1407)
at org.eclipse.equinox.launcher.Main.main(Main.java:1383)