The tab order property for forms is a nice addition (not sure when it was added, but I'm sure it was not there before unless I missed it). The only problem with it is that there is no 'OK' button. For ages I've been using the X button, and that causes it to cancel the changes.
In order to actually save the changes you make in this dialogue, you have to press the drop down button again to close it. I have to say that's a bit unintuitive at best. I actually thought it just didn't work for quite a while.
I think it just needs an OK button.