>After a question was recently closed the poster of said question started downvoting posts of everybody participating in the closure of his question.
>
>Is such behavior considered appropriate?

No, it's not.  Report it (like you did with this thread), and the mods will take a look.  It's been a while, but I recall there being a suspension category for this kind of behavior.  He certainly wouldn't be first to get a time-out for retaliatory voting.

On a related note, this type of poster is just another reason to think twice about commenting on bad, downvoted questions.  You end up becoming the target of some asshole's misplaced anger a lot more often than anything constructive comes of it.  ***Better to just downvote, (and/or) vote to close, shake your head at the fail and move on.***