I got the same problem, but solved it. Hit U button to show you what you gained when you leveled up. Then select New powers and it should let you upgrade again.
I have a similar question... I know how Skirmishes work by now, and how gold and items are aworder. What about if you're not in a party, and just happen to attack the same monster as someone else, and it dropps gold/items? Does each character involved get it's own drop, or is there only 1 drop and who ever picks it up…