This is extremely annoying behaviour. If you've voted to delete a post and then you press the delete button again, you can now rescind that vote, but then you can't vote again!
Because the button is exactly the same and there is always a confirmation popup when deleting, many people have made the mistake of accidentally retracting their delete votes unintentionally. This is unacceptable and needs a fix.
I propose to change the button text/look to make it more obvious that one has already voted to delete. Or maybe use a different popup. Or allow people to cast the vote again if they accidentally retracted it (but not after the post has been undeleted).