in reply to
Strange behaviour with modules
I'm puzzled about what you're trying to show us. I don't see a module called "Utility" on CPAN, and (assuming it's something specific to your app) I don't see any snippet to show what the "Single_Input()" function does. Could the internals of that module be relevant to the problem?
I also don't see "use strict" in any of your snippets. If you're allowing all variables to be global by default, then it seems like you're working against the general logic of modules: that they be independent and self-contained with regard to variables.
Of course, if you do use strict in all your modules, then I gather that you would (should?) also be using our $USERID; where necessary, to make sure that this variable is actually shared across modules as needed (as opposed to being global by default, or "strictly" distinct in each module).