Update on this: clearing the java webstart cache makes it work…better…sort of. It now actually works in developer without the debugger on. However, you have to click twice on the form to trigger the method. If you have the debugger on, only one click on the form to trigger the method.
With servoy client on the mac it takes two clicks on the form to trigger the method.
With servoy client on a PC, it works fine – only one click on the form to trigger the method.