Very simply, we had a party where we had our warrior tank afking / harrassing / trolling in Haukke hard mode. So, we went with vote dismiss. What do you know, the guy joins in-progress Haukke Manor and comes in our party again. After that he gets vote dismissed twice more but just joins the party once again, and then we have no vote dismisses left and it all was pointless.
In short, shouldn't vote dismiss prevent a player from joining the same instance again?