I presume that while out adventuring, if you hit your new level you can’t select feats until you return back to town? Is that how we have been playing it?
Soooo… based upon in game voice discussions, the answer tot he question. Is it can be allowed, on a case by case basis by the DM.
You level immediately upon gaining enough experience. You gain all skill improvements and feats immediately.
The only exception to this is adding a new class. That must hold until you can spend a week in town getting all the core training in.