So recently I managed to finish a round with about 98% of the exp needed to go from level 4 to 5 in power mode. So after I played a round and watched as my power levels XP bar fills up completely, Levels me from 4 to 5, fills all the way up again and empties with no reward.

I've also had this happen with my overall level, and had to re-earn level 13 as a result.