Good vs Excellent move? Same result or not?

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darkstar26

This is a position I had in a recent game. I thought of both Qc3+ and  Qd4+, but eventually played Qc3+ as I didn't see any difference. However, the game review seemed to think there was a difference with one I chose a +31.5 and other a +M7.  This seems a like a bug in the chess software. I can't think of anything I am missing, but maybe someone has an explanation. It is really strange since this is the first time a bug like this!

Comments?

Thanks.