A magic eagle-eyed commenter at Dead Homer Society noticed that whoever does the credits failed to doublecheck the spelling of Kristen Schaal:
Schaal seems perfectly fine with it, though:
Hey guys, they did misspell my name on The Simpsons. It's Schaal. But also- I was on The Simpsons. Still spoiled rotten w/ excitement.
— Kristen Schaal (@kristenschaaled) May 9, 2011