Not exactly sure what you mean by tag selector.
My process is to select the form in design or code view which than displays Edit Form, Edit Design, Edit Contents... in the Property Inspector. I usually click Edit Form at that point.
One related point.
Earlier today I moved my local copy of the site I'm currently having this problem with from a network drive to my internal and I now have about 75% of what I would consider normal functionality.
Location is not the issue in my opinion because I've had this problem many times with other sites regardless of where the site files are located.
One more potentially related point.
I have always had a problem with DW crashing out in the middle of a form development session. I find it necessary to do a little, click finish, save all than go back into the form again. At some point DW will still crash out so building a form takes far longer than it should.