Need Help! Bisect Inside Corner problem

Hi all -
Scratching my head on this one for a while now.... not really a showstopper, I just don't understand it.

I'm trying to cut these out of plywood, and I typically bisect the inside corners of notches for fit clearance. This one, however, doesn't want to recognize 'inside' as 'inside'. I export the faces out as DXF from Inventor, and open in BC v25 Pro. I've tried contouring the shape, reversing it, and running as straight lines.

Any ideas?
Thanks -

Attached Files

• ShelfA.zip‎ (55.8 KB)