Using 'parserPopUp.pl' and numbers in between quotes like $popup = PopUp(["Choose one", "0", "1", "2"], "1"); seems to turn the answer into index, and "0" is accepted as correct answer (which has index 1). Similarly, popup = PopUp(["Choose one", "0", "1", "2"], "0"); accepts "Choose one" as correct answer having zero index.
This is from LibraryUMN/algebraKaufmannSchwitters/ks_6_4_6.pg
I don't know if this is a new issue in V.2.19 but I used this problem before without students complaining. I rewrote the numbers to words and then it works correctly.