I wrote in Discipulos by accident when it's the dubject nominative -us. It never recognised my mistake even as a typo, and just accepted it as correct.
I don't think it should since they're different meanings.
I put Discipulis domi student (dative) which was accepted. Correct answer was: Discipulus domi studet. I did hear studet rather than student, but somehow persuaded myself that I heard Discipulis rather than discipulus.