My spouse and I have very little income (retired, with CPP/OAS). As part of the return, it looks like not only will I get all the taxes I paid in the year, back, as a refund, but also some more amount. That is because of some typical medical expenses over the last year. I thought the medical expense credit was a non-refundable credit (as in, it cannot exceed the tax liability).

Is it possible for me to receive a higher refund than the total taxes I paid, due to this medical expense credit, or does that indicate some sort of a mistake in the tax return?