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Not a blunder?

http://en.lichess.org/s0caFf3d

So, according to Stockfish, missing checkmate by underpromoting to the wrong piece is an inaccuracy instead of a blunder.

Not that it should be a matter of concern or anything, I stumbled upon this while messing with the analysis and just wanted to share it.
In some cases it would be considered a blunder, but not in this case.

A blunder gives too significant of an advantage to the opponent, but in this case, promoting to a bishop still does not give you opponent any more of an advantage, as the position is still +10 to white.

In this case, even if the pawn promoted to a pawn (which is of course impossible), that move would still not be considered a blunder. ;)
Also, promoting to a queen there would not be checkmate. The king can take whatever piece that pawn promotes to.
Promoting to either a queen or a bishop in this position is checkmate, try it, and checkmating(winning the game) is not a +10, it's off the charts(but in any case a swing from +10 to -1 IS a blunder) because you lose your chance of winning.

I think that labelling that as an inaccuracy is not right, because you turn your win into a draw at best (at best because I actually lost afer a couple of moves), which gives your opponent a huge advantage.

But anyway, as I said, it's just unimportant stuff.
I thought you meant that white playing 13. b8=B was the blunder, as that's the position when we click the link.

I see now that you were talking about black.

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