close Properties View in Seam perspective, open it, try to drag it and drop in some other place - I get Eclipse no response on any input.
look at screenshots, only Eclipse restart could help, reproducible only in Seam perspective. This exception is in Error Log:

Unhandled event loop exception

java.lang.ArrayIndexOutOfBoundsException: -1
at java.util.ArrayList.get(Unknown Source)
at org.eclipse.ui.internal.presentations.PresentationSerializer.getPart(PresentationSerializer.java:48)
at org.eclipse.ui.internal.presentations.util.LeftToRightTabOrder.restoreState(LeftToRightTabOrder.java:97)
at org.eclipse.ui.internal.presentations.util.TabbedStackPresentation.restoreState(TabbedStackPresentation.java:206)
at org.eclipse.ui.internal.presentations.PresentationFactoryUtil.createPresentation(PresentationFactoryUtil.java:58)
at org.eclipse.ui.internal.PartStack.createControl(PartStack.java:571)
at org.eclipse.ui.internal.PartSashContainer.replace(PartSashContainer.java:794)
at org.eclipse.ui.internal.ViewSashContainer.replace(ViewSashContainer.java:316)
at org.eclipse.ui.internal.PerspectiveHelper.addPart(PerspectiveHelper.java:377)
at org.eclipse.ui.internal.Perspective.removeFastView(Perspective.java:1192)
at org.eclipse.ui.internal.Perspective.removeFastView(Perspective.java:1167)
at org.eclipse.ui.internal.WorkbenchPage.removeFastView(WorkbenchPage.java:2988)
at org.eclipse.ui.internal.FastViewManager.makeFast(FastViewManager.java:380)
at org.eclipse.ui.internal.FastViewManager.removeViewReference(FastViewManager.java:360)
at org.eclipse.ui.internal.PerspectiveHelper.derefPart(PerspectiveHelper.java:714)
at org.eclipse.ui.internal.ViewSashContainer.derefPart(ViewSashContainer.java:278)
at org.eclipse.ui.internal.PartSashContainer.stack(PartSashContainer.java:1244)
at org.eclipse.ui.internal.PartSashContainer.dropObject(PartSashContainer.java:1210)
at org.eclipse.ui.internal.PartSashContainer$SashContainerDropTarget.drop(PartSashContainer.java:132)
at org.eclipse.ui.internal.dnd.DragUtil.performDrag(DragUtil.java:134)
at org.eclipse.ui.internal.FastViewPane$2.dragStart(FastViewPane.java:161)
at org.eclipse.ui.internal.FastViewPane$2.dragStart(FastViewPane.java:136)
at org.eclipse.ui.internal.presentations.util.TabbedStackPresentation$1.handleEvent(TabbedStackPresentation.java:118)
at org.eclipse.ui.internal.presentations.util.AbstractTabFolder.fireEvent(AbstractTabFolder.java:269)
at org.eclipse.ui.internal.presentations.util.AbstractTabFolder.fireEvent(AbstractTabFolder.java:282)
at org.eclipse.ui.internal.presentations.util.AbstractTabFolder.handleDragStarted(AbstractTabFolder.java:366)
at org.eclipse.ui.internal.presentations.util.AbstractTabFolder$2.handleEvent(AbstractTabFolder.java:67)
at org.eclipse.ui.presentations.PresentationUtil.handleMouseMove(PresentationUtil.java:110)
at org.eclipse.ui.presentations.PresentationUtil.access$4(PresentationUtil.java:95)
at org.eclipse.ui.presentations.PresentationUtil$2.handleEvent(PresentationUtil.java:63)
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:2640)
at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2604)
at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2438)
at org.eclipse.ui.internal.Workbench$7.run(Workbench.java:671)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:664)
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)