John,
I have trouble with %il because the limits are not dynamic, and also you can't have the low and high limits the same. Often, I check the limits in the callback - they can then be dynamic, or the same.
The business of using proxy data means that you do have a one-step possibility for undoing changes. You can always go back to the previous save.
In particular, the Windows MDI (multiple document) business requires a complete data set for each 'document'. I normally reckon that users of scientific software can't do MDI, because you have to keep too many ideas in your mind simultaneously.
Eddie