shutDownRequest fails to work?

[Barry Levine]

I have an OSX stack that, when part of an app, is using the following 
handler in the stack script to intercept the Quit command:

on shutDownRequest
   if the platform is "MacOS" then
     answer information "Are you sure you want to quit?" \
     with "Quit" or "Don't Quit"
     if it is "Quit" then pass shutDownRequest
   end if
end shutDownRequest

The first time I select "Quit" from the app menu this handler is called 
and I can cancel the Quit. However, the next time I select "Quit" from 
the app menu (during the same session), the app just quits without the 
intervening dialog.

Any ideas?
(OSX 10.2.6, Rev 2.0.2)

Thanks,
Barry