As discussed before, clicking upvote (for certain recent "hot" questions) might randomly prompt one to share a link:
According to Jeff this is by design, which I think is really double bad. Now SE has random (and) unexpected behavior! It also means you cannot use the keyboard arrow keys to scroll down to the answers (as the focus is on the permalink).
It is unexpected behavior because the up-vote and the [link] are unrelated, but all of a sudden the exact same visual effect appears on screen.
This is really easy to solve. Instead of popping up the permalink, a yellow notification box could be popped up with a suggestion to use the [link] link. Maybe at the same time popping up the link a little as well. The non-blocking notification could be visible during some time.
Edit The yellow notification box could also contain the permalink as per Michael Mrozek's example.
This is really not such a big issue, but eliminating small pains result in happier users.