pq11059.st DEFERRED PROCESSING OF A PUSH BUTTON CLICKED 
               EVENT CAN CAUSE A WALKBACK

The method AbtPushButtonView>>#userClicked:clientData:callData:
processes the clicked event for a push button.  This processing is 
done in a block which gets deferred.  Before the clicked event 
processing is invoked, a check is made to ensure the handlers are 
not nil.  This check occurs outside of the block which leaves a small 
window in which the handlers can be removed before the block is run.
If this happens, you get a walkback. 

To correct this problem, a check is added to block to make sure the
handlers are not nil.

File in pq11059.st to fix the problem.