I am getting experience during a NG run with my NG+ character. Even past level 20. I leveled from 20 to 22 during the last NG run. Is this intended? I thought my char could only get experience in a NG+ run for levels 20 through 25 and NG++ for 25 through 30 etc.

The way I understand it, unlocking NG+ also "unlocks" the ability to level to 25; you can still gain the XP on normal runs, but you can't break past lv. 20 without beating the game on normal, and so on.