Today I was playing infection, and voted. I gained 3 levels of XP, and hit level 80. Then after that match was over I those 3 levels.
You must be on infection for the levels from voting to count/stay. If you vote on any other game mode or off-line you will lose the levels you got from voting, only the levels from voting. This does not apply to other game mode, as you can still get the vote rewards even if you voted off-line
This is a glitch. The admins are not going to give you three levels. Next time, vote while you're a human. Closing.