All I know is what I read in the instructions. 

"If you are a PA resident who does not have any PA income (loss) to report, you do not have to file a PA tax return, even if married to a person who must file a PA tax return."

"You and your spouse have the option to file separate returns. However, you and your spouse must file separate returns if: . . .

6. One of you is a PA resident and the other is not. However, you can file jointly if you both elect to file as PA residents and meet all other requirements for filing jointly."