Well, just from the Merriam-Webster entry linked above, plus Wikipedia: It's been spelled out as "Habsburg" since late 13th century. Just because around 1861 someone misspelled it as "Hapsburg" does not mean we should perpetually repeat this error.

You know how this works: human life is short, and our memory is even shorter, so it takes just one uneducated idiot to make a spelling mistake, then dozen of other idiots to repeat it, and after hundred years the mistake becomes a time-honored tradition.