I use xp/FMP11 and do not see this problem.
If you create a brand new file with just a field or two, does it exhibit the same behavior? (might be a problem with your file)
If you create a new layout from scratch in your existing file do you see the same problem? (might be a problem with the layout)
IT HAPPENS ON ANY NEW FIELD.
I HAVE TRIED FP 11 UP GRADE & FULL VERSION. SAME PROBLEM
New field in the same file or a new file?
New field in a new layout or the same layout?
If you get the same behavior with a brand new file, then the issue is with either your computer or your installation of filemaker. If it is only with a specific file or specific layout, you may have a corrupted file or layout. Sometimes file damage issues are hidden until an upgrade or OS change reveals them.