It looks like everything happening in a LayoutDialogForm is deferred, so the UI is gone before any handlers are invoked. This is true even if you explicitly replace the MayaEvents with Events, which makes no sense to me. Need to investigate further
ah... so for some inexplicable reason, inside a layout dialog the test isinstance(Event(), Event) returns false - the events were not getting assigned at all!
It looks like everything happening in a LayoutDialogForm is deferred, so the UI is gone before any handlers are invoked. This is true even if you explicitly replace the MayaEvents with Events, which makes no sense to me. Need to investigate further