Dwarven Ale curse Munchkin
It is not in the FAQ. But the Temporary Amnesia is mentioned on a forum.
Question:

Had a little debate in a game today over this one...
I say that since the card (Temporary Amnesia) says you are Human &quot;for all purposes&quot;, that trumps items like Casting Couch for special powers and Fake Ears and
Fake Beard for the sake of monster bonus/penalty and Race/Class
specific items.
The other side says that those are simply items that override or
sidestep your actual Races/Classes and are thus not affected by
Temporary Amnesia. You're actually a plain old Human, but if you put
on Fake Ears, monsters will think you're an Elf, and so on.
Which is right?

Answer

Your friends are right. Fake Ears/Beard don't actually change your Race; they just change the way it appears. The fact that you don't remember your real Race doesn't affect how those Items work.

This implies that as long as Temporary Amnesia is in effect, you are not a dwarf so the +4 does not apply. But if you wear a fake beard, the +4 again works.