If the hatter is mad, just not termed by Carroll such, it is only inaccurate if you Capitalize 'mad'. So it is perfectly correct to refer to the mad hatter's tea party. If you want to call out the party, then Mad Hatter's Tea Party would be the way to go, inasumch as to term it: mad Hatter's Tea Party might be taken to refer to the fact that the party was mad not its participants.

So I don't agree with the lead post, though I do share the attitude as I have my own 'buttons' just can't think of them at the moment.