Users can add a poll when adding a picture to their Instagram "story", and can see what their followers choose.
Many users said they did not realise their choice would be visible to the poll instigator, and some said they had made embarrassing mistakes.
Instagram did mention that votes would be public when it announced the featureon its blog and in the app.
However, not all have watched the Instagram video to learn how the feature works.
Some people said they had cast questionable votes on polls, such as "Do I look cute?" or "Do you like my art?" without realising their choice would be shared.
Rival social network Twitter lets people create polls, but it does not reveal how people voted.
Instagram has not yet responded to the BBC's request for comment.
