So this is a weird thing I'm seeing only with the F-16. I use Button 2 on the throttle as a modifier button. For the F-16, after I press the modifier button and then use another button to select a function, it will continue to activate modified functions, even though I'm no longer pushing the button, until I press and release the modifier button without pressing any other key. I can make this happen in the control setup pages, i.e. I don't need to be flying a plane, and it is consistent and only happens with the F-16. I'm able to get normal function, using the exact same key commands, with a M-2000C or an F/A-18.
This is an odd "bug" and hopefully I've been able to successfully communicate what I'm observing :)