The Last Hope artifact merchant shouldn't make anti-magic mindstars unless the player has the antimagic tree, or has no runes/spells/arcane artifacts equipped.
My Ghoul Doomed just forked over 4000 gold for an awesome but unusable mindstar....
Yes this happens but it's not considered a bug AFAIK. All the more reason not to play undead characters. I for one would like to see this behaviour gone, though. I once had a skeleton rogue who got two antimagic merchant items in a row (which were the only ones I could afford in that game).
EDIT. What I meant was, I'd rather have the merchant not produce AM items for undeads specifically. In reality, undeads won't be using AM-items ever (same could be said about shalore, though, but at least they can use infusions).
EDIT 2. I'd be totally fine with not giving AM items to arcane skilled characters in general too.