I'm asking no question here - just trying to share some experience. The implied question would be "am I insane or what".
I had a container with an optiongroup and a command button. The commandbutton should be disabled if the optiongroup has a nondefault value (which was stored as a property of the containter). The code to enable/disable the button was in the optiongroup's InteractiveChange. There was a whole array of these containers, spread across three pages of a pageframe - completely data driven. Most of the containers had the commandbuttons invisible.

Now the problem: depending on where and how did I arrange the code, the optiongroup would sometimes work properly (usually there where the commandbutton was invisible), or else would quickly revert to the old value when clicked. Initially this happened only for the optiongroups whose containers had the commandbuttons visible, then it got fixed when I moved the code a little, then came back (for all of them) after more fixing of the code, then settled on just those with commandbuttons. What which eventually made it work was the old Indian trick "This.value=this.value" at the end of optiongroup.interactivechange (which was basically calculating one logical and set this.parent.cmdbutt.enabled=lThisLogicalVar).

Besides the usual "hope this helps somebody", I'm really curious to know if anyone else had a similar experience.