I'm a graduate student doing research in physics. Through this month, I had an NIH grant through the Engineering department. I was also covered by my advisor's NIH grant in physics, with possible backup from the Physics department in case of a shortfall.
This month, I was paid twice, for different amounts—once, apparently, from the the Engineering grant for work done in Engineering, and once from the Physics department for physics research. The problem is that, effectively, they're the same research. I wasn't doing twice as much research, although there were minor additional projects and requirements for the engineering grant. This is the last month of the engineering grant, which may explain the overlap.
How should I proceed?
Keep the money? Could the university demand it be returned at a later date? Might I not get paid next month?
Keep only one of the payments, and try to get the other back to the university? Which one?
Return them both and try to get paid again?