Problem with counting numbers of groups in a stack

[Stephen King]

Hi all,

I have just come across a problem with counting the number of groups, between the IDE and built application. 
I have a small stack that has 20 groups (listed in the App browser). It has a main and sub stack with no groups on the substack. There are no plugins in use (according to the App browser).

When I use 
"put the number of groups into NumF"

In the IDE I get 20, as expected and the App runs fine, but when built I get 21 groups reported. This crashes my App as there is no group 21 for it to reference. Debugging the built app shows this is the reason for the crash.

I have also checked this by changing the code to add 
"put NumF-1 into NumF " 
immediately after the number of groups statement. The App no longer runs OK in the IDE but does run OK when built! This is a sort of workaround, but not understanding the cause is a bit worrying.

Any ideas?
I am using 2.1.2 and Win XP home

Any help appreciated.
Cheers
Steve King