BUG:
After using form field auto detection, the program crashes to desktop (without any errors) as soon as any field is clicked on or when attempting to add a new field. Leaving the Prepare Form tool works as intended; the crash only happens when attempting to work further with the tool. Leaving and reentering the tool still causes crashes.

WORKAROUND:
The only way I've found to prevent this is to use the "Export Data" tool (the .fdf export one). Once the data is exported, things seem to work fine, without even requiring a re-import or anything like that.