I have heard that there is atreasury box somewhere in the keep. (Some suggested collected taxes are stored there.) It is just speculation, but what if y payment from hirelings is deducted from this treasury and not from your party cash? Perhaps if you have to pay more for hirelings than you earn taxes than some of the hirelings get the "unpaid" status? Does any body know where this treasury chest is exactly?
I have found the treasury box, but I could not put money in it, so that is not the solution.