You don't need to create your own interrupt action (ON ACTION interrupt) - BTW this would bypass the default behavior.
GDC creates its own LocalAction (as well as editCut, editCopy...) name interrupt (looking into actionDefaults for the decoration and key accelerators).
If any action view (button, toolbar item...) has the same name, i.e. interrupt, it will be bound to this localaction.
The localaction is activated when the runtime system is buzy (i.e. either when it sends a message "I'm busy", or when it does not answer for half a second).
If the form button is working correclty but non the toolbar button, this means that:
- the internal interrupt mechanism is working
- the toolbar item may not be correctly attached to "interrupt" action.
The best would be to send a test case, either on this forum, or directly to your support center.