with level 5 unarmed skill and krav maga, my character uses leg block against every attack. he continues to use them even when the legs are at almost no health. he also never uses arm blocks. my guess is that when the game calls for an arm block it somehow becomes a leg block.
That does indeed sound like a bug. Alternatively, your character may look something like this:
But in all seriousness, thank you for your report!