No experience here with Mattercontrol, but I have seen this happen in Slic3r. (not sure if you are using that engine) In Slic3r’s preferences window there will be “Auto Center Parts” option. If this is activated, it will automatically put the object in the center of the build area according to the slicing profile.
This is about the only thing I can think of without any experience with Mattercontrol, I hope it helps!