I know the topic is a little old but I found something strange (but positive) with the registering callback node.(LabVIEW 2012)
I wanted to create a way to monitor the lost focus event. This event is not native in LabVIEW. So I tried to register a callback to react to a pane: mouse down event. When this event is triggered I check which control has focus and execute some code.
In .vi form it doesn't work but as an executable it works great. I attached a simple code. Have a look to the init ability. Tried the unitTest.vi then the UnitTest.exe.
Romain
Xcontrol with focus lost event.zip