I think the best approach is to store the value to a property rather than simply setting a flag in InteractiveChange. Two reasons:

1) You can avoid considering a field changed if the user simply changes the field to the same value.

2) More importantly, dropping down a combo always fires InteractiveChange, even if no value is clicked on (to say nothing if the _same_ value is clicked on).

After discovering this with combos (where I want to avoid Requerying other combos if the first one didn't change), I'm gradually adding value saving and comparison to all my base control classes.