Gensor,
Did you by anyway miss my post no. 3.
I'm 99% sure the problem is not with your application, but with the OS/ extenal factors. The END statement terminates the application instantly & unconditionally (though I won't recomment using it). So whether it is a circular reference or resources not released, this problem shouldnot occur.
The surest way to confirm what I said is to try your app on another system. In case the problem is still there, your program is to be blamed, incase the problem goes away your OS is to be blamed.

Pradeep