Here's a guess: It sounds like your postprocessor might be set up to arc off and around when it comes to a sharp external corner. The reason is that your machine can't decellerate fast enough to get around the corner and overshoots, so you'd end up with a little wedge shape at each corner if you ran like that.
Whoever wrote your post tried to get around this by forcing the code output to do a little loop around so you would get a sharp corner. i.e., it the cutter arcs off, and then arcs back on again.
If that's the case, you need to use G61 (exact stop mode) to force the cutter to decelerate before it reaches the corner and stop exactly where you are telling it to.