Hey The_Falck,
We are aware that some players are experiencing a "mirroring" issue while playing split-screen/sharing console and Infinity Ward is investigating. In the mean time, try playing an online match and see if your stats return to normal as well as logging all accounts out of the console and clearing the cache. Please private message me the following:
As of now, we don't have any updates, but more information is needed to get a better understanding of what may be going on. Can you please provide the following information:
-What console are you playing on?
-Can you please provided us the affected Gamertags/PSN ID's?
-Explain which usernames are being overwritten
-Were you playing split screened?
-If so, who was player 1 and who was player 2?
-Were you partied with someone on a separate console?
-Are you sharing a connection?
-or are they in a different household entirely?
Thanks,
^MC