Unranked servers aren't supposed to give you experience and levels, but my friend levelled up on an unranked server. ???
Maybe your unranked exp can be higher than your ranked exp? Is that how it works?

This is one of the things I'd like some official clarification about, but no such info seems to be available.

I, however, think that experience is experience no matter what kind of server you get it from and as such, XP's should accumulate on unranked servers as well. I've got the impression that this is the case, too. I think I get (and lose) XP from both ranked and unranked servers.

Then again stuff like total public K/D ratio should not be affected when playing on an unranked server.

From what I've seen, you do get xp on unranked, but it's just the xp of your score in the game, you don't get any armor/power/cloak xp, nor do any stats from the game go on your profile.

From what I've seen, you do get xp on unranked, but it's just the xp of your score in the game, you don't get any armor/power/cloak xp, nor do any stats from the game go on your profile.
It's a bit silly if you can get "normal" exp without getting armour/power/stealth exp in my opinion...

Well I tried it and it resets after you log back in

Yeah it resets, after you leave the server, I learnt that the hard way after levelling to 30 on an unranked server