Sometimes it allows either simple present (eats) or progressive (is eating) and sometimes it marks either as wrong. There appears to be no pattern which it wants then, and either makes sense. Are there rules about which is right when?
You must have encountered some kind of bug. Swedish doesn't distinguish between simple present and proggressive present, they're the exact same verb in Swedish. For example, en hund dricker vatten = a dog drinks water = a dog is drinking water