This is a relatively common issue that has been discussed within several other forum topics. It has to do with each ModelState potentially having a different value for each Parameter. And also has to do with the 'member edit scope' or 'edit factory scope' vs 'edit member scope' setting, which dictates whether the changes you make will effect only the 'active' ModelState member, or if it will effect all ModelStates. If the edit scope is set to active member scope, then you change a parameter's value, that means you only changed that parameter's value in the active ModelState, but not in the other ModelStates. So, when you use that action as a trigger to change which ModelState is active, it may activate another ModelState OK, but the newly active ModelState may have a different value for that Parameter that you just changed the value of, because the change was made to the previously active ModelState, not to the newly active ModelState. To avoid this, set the edit scope to 'all members' or 'factory scope'...that way your parameter value changes will effect all ModelStates the same way, at the same time. If that is not your goal, then it might not work for you.
Wesley Crihfield

(Not an Autodesk Employee)