It is a known issue. See **#22485**: RButton can be clicked mutliple times during event handling were it should be blocked
You can track the bug within [soreconect][1]. As the this is known since a longer period of time, but not yet fixed, I would suggest that you implement a workaround. You could introduce something like a "buttonClicked" flag on the process data and only proceed the event execution, when the flag does not indicate, that the event has already been executed.
[1]: http://www.soreco.ch/soreconnect