Any cutting tool I can think of causes some compressive forces when it cuts. A planer is a good example. You can run a board through at a single setting and it will always take a little more off on the second pass. The same thing is true in milling metal which is why many precision parts are ground to size instead. The same may be true of your lock miter bit, especially without feather boards.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.