From what I read, it was intentional and based on theory,
and is used only in Germany.
>
>Magnus is right. B is right (as in A, B, C ...).
>H is the fault of some monk who mistook a B for an H
>when he copied sheet music centuries ago,
>and this error was propagated in Germany (Europe?)
>ever since. Or so I've been told.
>
>But I've learned it as H, and every time I see a B
>my brain interprets it as B_flat. (This is is the
>∗real∗ bad thing, that they assigned the letter B
>to something different afterwards. Anybody
>knows why on earth they did ∗that∗ ?!)
http://sonic-arts.org/dict/german-h.htm