It's just wages. I don't get far enough to look into missions, and I don't do Arena too often, but I did notice it added afterwards.
I'm sorry Daku, I've tried everything I can think of, and I can't reproduce the problem. My only suggestion will be to make sure you have the most recent version - though I don't think I've changed anything relevant to wages. If other people report the same problem, it will help me figure out what the issue is. Right now, I'm afraid I can't find any problem.