Bevel Button fires twice with menu (Cocoa)

Hi, I’ve a Bevel Button with Menu. If I move my window near the edge of the screen then the menu (which is on the right) is over the Bevel Button. See screencapture

Once launch the Thread affected to the menu “Comptes inclus”, then the BevelButton become “Stop” (to stop the Thread if user click).

The problem is that if when I choose the menu “Comptes inclus” with the mouse over the “C”, then over the Bevel Button itself, it fires again and then stop the thread. If I select the menu “Comptes inclus” with the mouse over the “us” (the end of the sentence, then not over the Bevel Button, then it works).

I have a workarround using a Static and Ticks, but I wonder why the Bevel Button is launched twice.

The problem is because I remove the menu once selected one menu.

I made a small program to reproduce what I try to explain :