Final Cut Export takes ages when magnetic mask is already calculated!

I have a really weird issue in Final Cut Pro 11. I calculated the magnetic mask and it took some decent time (but reasonable because it's a computational heavy) now when I export the clip (no matter I select same as source or h264 etc. it takes even longer to export than to calculate the magnetic mask in the first place. Is this some kind of bug where the magnetic mask gets recalculated on export again? This is insane the work should be already done. Just to be sure I exported without magnetic mask applied and once with and the time difference on export is like 50-100x longer! how is this possible?