It appears Linuxcnc applies path blending to all moves including G0 moves. That is not how I thought the planner was supposed to work. I thought that all G0 moves were supposed to be pure positioning moves and behave like a G61 move. In my humble opinion this is a bug.
Your config probably has G64 as a default setting, you can either change that to G61 or add a P tolerance to the default G64 setting. That should straighten out your corners.
