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That sounds exploitable. People would strategically vote "I don't understand" to delay the initiative.

Why do that instead of just "no"?

Because likely to elicit reworking of the proposal you would need less than 50% of the vote. To defeat the proposal you need at least 50%.

you could still deal with that. one option would be to just go for the outcome with the highest percentage, instead of the simple 50% majority.