If you upvote a "hot" question SO will sometimes open the "share this link" as by design: Upvote = Permalink
Firstly, I'm not that comfortable with this since it makes it impossible to scroll down the page using the arrow keys. Also pop-ups (that causes the window to lock to it) should in general be avoided IMO. Maybe this could be solved by adding a text below the link instead of locking the window to the pop-up?
Secondly, another issue with this pop-up is that if the question is long enough to produce the scroll bar, then the pop-up will cause the page to scroll to that part of the page. Also annoying if you're in the middle of reading.
Thirdly, if the user is almost out of upvotes for the day, an orange notification will tell that to the user. The scroll will cause the user to miss this notice. This might not be a big problem but I thought I should mention it anyway.