It would be nice if XMM would immediately warn that the size limit for a field is reached or exceeded while editing a record.
I've noticed that when I copy and paste to much information into fields the only actual complaint from XMM will be a Jet / VB message in the status line after closing the edit window. It seemed that none of the changes made for this record (not just the ones where too much data got pasted in a field) were saved.