Sometimes on a vocab quiz I get a sentence with a verb that I know, but a verb form that I haven't yet seen in a lesson. I'm still on the 17 beginner lessons, but I'll get sentences with "passive" or "volitional" forms.
Is this a bug? Or is it testing to see if I can recognize the verb even though it's conjugated differently than I've ever seen before?
If you're talking about vocabulary sentence questions with Pro, AFAIK they're selected based on your vocabulary knowledge and don't account for your grammar knowledge at all, so they cannot be narrowed down to only conjugations you've seen before. If it bothers you, you can turn sentence questions off until you know more verb forms.
You can do what others do, which is tap the ? button and submit a quiz report. All sentence selections are done by humans (me), so there is always the chance that inappropriate (in the sense of too high of a level) content is put into the quizzes. I do regularly make adjustments to sentences based on reports like this :)
