DnD over VPE source part fails under Mac OS X and partially frozen UI

java.lang.IllegalArgumentException: Index out of bounds
	at org.eclipse.swt.SWT.error(SWT.java:4472)
	at org.eclipse.swt.SWT.error(SWT.java:4406)
	at org.eclipse.swt.SWT.error(SWT.java:4377)
	at org.eclipse.swt.custom.StyledText.getLocationAtOffset(StyledText.java:4372)
	at org.jboss.tools.jst.web.ui.internal.editor.jspeditor.xpl.StyledTextDropTargetEffect.dragOver(StyledTextDropTargetEffect.java:157)
	at org.eclipse.swt.dnd.DNDListener.handleEvent(DNDListener.java:84)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
	at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4230)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1491)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1514)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1499)
	at org.eclipse.swt.widgets.Widget.notifyListeners(Widget.java:1299)
	at org.eclipse.swt.dnd.DropTarget.draggingUpdated(DropTarget.java:319)
	at org.eclipse.swt.dnd.DropTarget.dropTargetProc(DropTarget.java:452)
	at org.eclipse.swt.internal.cocoa.OS.objc_msgSendSuper(Native Method)
	at org.eclipse.swt.widgets.Widget.callSuper(Widget.java:227)
	at org.eclipse.swt.widgets.Widget.mouseDownSuper(Widget.java:1121)
	at org.eclipse.swt.widgets.Tree.mouseDownSuper(Tree.java:2047)
	at org.eclipse.swt.widgets.Widget.mouseDown(Widget.java:1113)
	at org.eclipse.swt.widgets.Control.mouseDown(Control.java:2569)
	at org.eclipse.swt.widgets.Tree.mouseDown(Tree.java:2015)
	at org.eclipse.swt.widgets.Display.windowProc(Display.java:5692)
	at org.eclipse.swt.internal.cocoa.OS.objc_msgSendSuper(Native Method)
	at org.eclipse.swt.widgets.Widget.callSuper(Widget.java:227)
	at org.eclipse.swt.widgets.Widget.windowSendEvent(Widget.java:2130)
	at org.eclipse.swt.widgets.Shell.windowSendEvent(Shell.java:2337)
	at org.eclipse.swt.widgets.Display.windowProc(Display.java:5756)
	at org.eclipse.swt.internal.cocoa.OS.objc_msgSendSuper(Native Method)
	at org.eclipse.swt.widgets.Display.applicationSendEvent(Display.java:5193)
	at org.eclipse.swt.widgets.Display.applicationProc(Display.java:5342)
	at org.eclipse.swt.internal.cocoa.OS.objc_msgSend(Native Method)
	at org.eclipse.swt.internal.cocoa.NSApplication.sendEvent(NSApplication.java:128)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3695)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$4.run(PartRenderingEngine.java:1127)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:337)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1018)
	at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:156)
	at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:654)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:337)
	at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:598)
	at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:150)
	at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:139)
	at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:134)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:380)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:235)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:497)
	at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:669)
	at org.eclipse.equinox.launcher.Main.basicRun(Main.java:608)
	at org.eclipse.equinox.launcher.Main.run(Main.java:1515)