Same error here.
inserted behaviour on an Update page, no problem.
went to insert on Insert page - initially cursor was not in form and I got an error message asking if I wanted to add a form. Clicked No, moved cursor, went to insert progress bar, same error.
Deleted cache - same error.
It may be that I need to reboot the computer and delete the cache again but really, this stuff gets old.
It is clearly a bug and needs to be fixed.