Thank you for giving me the opportunity to assist you. I will give the best answer that I can with the information provided.
Unfortunately yes, that is what they expect, and it is a trap--but think of it this way, if you were married and purchased two homes, you would have only been eligible for one $7500 credit.
There are several exceptions to paying the credit back all at once, such as death, divorce, military orders, etc. But none that applies to your situation.
The rule for the 2008 credit was that if you stopped using the home as a main home, the entire balance of the credit (amount unpaid) would become due that tax year. Involuntary conversions are condemnation, disaster---or something like that, not a change in marital status.
Hopefully, if you sell one home, you may have the money to pay the credit back. If you sell the home at a loss--you may not have to pay the credit back at all, since the credit payback will be limited to the amount of gain on the sale.
Please let me know if you need further assistance.