I have noticed this happen, also sometimes you cannot even select the bend line to dimension to.
Yep I think there is definitely something wrong with sheet metal in 2013.
Not at all confidant about using this function at the moment.
I am experiencing the same thing with the latest service pack 3, since upgrading to 2013 this has been an issue. Also, the profile sketches from forming tools are not wanting to show up in the flattened state even though that is how I have the options set. I am going to start upgrading every year after about the 4th service pack has been released, this is advise that other users have said.
Don't see it here on SW2013 SP 3.0. Can you attach a sample part file and drawing to test.
I have also seen this happen a number of times in 2013. Unfortunately, I don't recall specific examples, but it basically causes your good bend dimensions to go dangling for no apparent reason.
Possibly related to this: I have also had bend dimensions that went from the bottom edge of the part to the bend line, suddenly flip over from the top edge of the part to the bend line. I can't recall the exact sequence of commands that caused this, but will try to keep it in mind if I see it again.