You know, I'll answer the question, but one of the reasons I'm hesitating right now is that it depends on the relative numbers of these three groups, and that's not constant. In a situation where you have a clearly stated question and you have leaders of political parties or interest groups who are well known, who are arraying themselves for and against in some way that voters see as coherent, you're not going to have as many people in group one. You're not going to have as many people who are confused.
Where group one can cause trouble is when things get hard for them to comprehend. This can be a situation where the question is so complicated that the interest groups, the traffic lights that they're looking for, are not working or are sending inconsistent messages. Group one can't really take these information shortcuts and make the same decisions. That's when things get problematic.
I will say, though, that as a general rule, when voters get concerned or confused, they generally vote “no”. If you want to think about how they're most likely to cause trouble, it would be just by voting no.