all the skunks and mushrooms are annoyingly disease resistant, one timed i had to cast Cessation of Cor 6 times and still didn't land, could have taken more but i gave up after the 6th resist.
I believe you're confusing this skunk with the funky skunk. The funky skunk is a named and spawns out in the courtyard area like all the other skunks. He sees invis, the rest of the non-named in the courtyard do not.
I've spent more time in mischief than any sane person should, and I can't ever recall a non-named seeing invis there.
I found one of these skunks last night who saw through invisibility: I'm guessing that maybe he was the placeholder for the named skunk? It was definitely Fetid and not Funky :).