OK, another one from the Alpha-testing:
the last field in the form is a URL. User types in an erroneous URL (like without the http://), but because it is the last field on the form, he clicks Save. Now the field gets a red border, but prob. too late. This results in a choke-up, you have to kill the tab.
In a more roundabout way: this could happen on any field. Question: how do I check form field validation=OK before I allow to Save?