When a user with low rep clicks on "Upvote" on an answer to his own question he is shown a hint saying that he could just as well accept this answer. But when he accepts an answer without upvoting it he is not shown anything even if he has enough rep to upvote.
Add to this that users with rep below 15 can't upvote - so the users starts in the "can't upvote" state (if they click "upvote" the site shows an error message), then their rep grows and they now can upvote, but noone tells them about it. This is not very good - many users ask only a few very tough questions that get very low attention and thus those questions sometimes are accepted without even a single upvote.
It would be great if all users that meet the requirements for being shown "you can as well accept this answer" and have enough rep to upvote are shown a hint like "you can upvote this and other useful answers" when they accept an answer without upvoting it first.