Miter cut in sheet metal flat not working

[Atlas_8850]

I'm trying to make a sheet metal part with some bent flanges, but the miter cut option in the "Flat" tool doesn't work on one of my corners, as shown in the attached image. Any idea why the left corner fails but the right corner works? Creo 8 and Creo 9. 

[kdirth]

Which version of Creo are you using?

I am on 7.0 and cannot recreate the flats you have.  However, looking at the image, I would guess that the left corner is across an opening while the right is a continuous wall.

[Atlas_8850]

I'm using Creo 9, but this same thing was happening in Creo 8.