I'm having the same issue. Went from LV21 back to 4 on my first day. Went for P1 LV45 last night, back down to P1 LV29 today. I just wanna progress naturally and legit like the good ol' days and I'm worried about MW3 doing the same since progression is slower on there.
Until we get a definitive answer: I found playing one public game after you change class/scorestreak/profile stuff can help 'save' your progress before you exit the game. But I don't know if it's 100% reliable.