To recreate:

• With no hybrid mobile engines defined
• Preferences->Hybrid Mobile-> Engines
• Click on "remove" and the exception is logged - no feedback is provided to the user in the UI

!ENTRY org.eclipse.ui 4 0 2015-04-28 14:30:25.700
!MESSAGE Unhandled event loop exception
!STACK 0
java.lang.ClassCastException: org.eclipse.thym.core.extensions.PlatformSupport cannot be cast to org.eclipse.thym.core.engine.HybridMobileEngine
at org.eclipse.thym.ui.internal.engine.AvailableCordovaEnginesSection.handleRemoveEngine(AvailableCordovaEnginesSection.java:606)
at org.eclipse.thym.ui.internal.engine.AvailableCordovaEnginesSection.access$4(AvailableCordovaEnginesSection.java:598)
at org.eclipse.thym.ui.internal.engine.AvailableCordovaEnginesSection$5.handleEvent(AvailableCordovaEnginesSection.java:378)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4477)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1322)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3815)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3425)
at org.eclipse.jface.window.Window.runEventLoop(Window.java:827)
at org.eclipse.jface.window.Window.open(Window.java:803)
at org.eclipse.ui.internal.dialogs.WorkbenchPreferenceDialog.open(WorkbenchPreferenceDialog.java:211)
at org.eclipse.ui.internal.OpenPreferencesAction.run(OpenPreferencesAction.java:63)
at org.eclipse.jface.action.Action.runWithEvent(Action.java:473)
at org.eclipse.jface.action.ActionContributionItem.handleWidgetSelection(ActionContributionItem.java:595)
at org.eclipse.jface.action.ActionContributionItem.access$2(ActionContributionItem.java:511)
at org.eclipse.jface.action.ActionContributionItem$5.handleEvent(ActionContributionItem.java:420)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4477)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1322)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3815)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3425)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$4.run(PartRenderingEngine.java:1112)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:337)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:993)
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:138)
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:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:648)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:603)
at org.eclipse.equinox.launcher.Main.run(Main.java:1465)
at org.eclipse.equinox.launcher.Main.main(Main.java:1438)