There are also problems with buying items from her (as in buying a weapon but gaining another one instead)
Well, I've registered especially to report that so I won't miss a chance to do it ;-) Ok, well...
:

: The bug is actually that instead of buying the item selected you get the item listed two slots above, but for the price of the selected item. So you can use it to get almost all the stuff from the merchant for virtually no gold...
:

: And one more thing: you can use, e.g. throwing daggers to buy all the things above it, and when you finally reach , e.g. missiles +4, you can double-click the daggers and choose *much* more than those 20 the merchant has. I bought a few hundreds of those missiles and the list of item at the merchant's showed 'Missile +4 (-290)' or sth like that.
Thank you for attention ;-)