I've joined two separate instances personally (and had players in-game say they've seen it as well) where during this instance the second wave never spawns.
Did a search in this forum, but didn't see a report of this - so sorry if it has already been reported.
Also, I wasn't able to put in a bug report in-game as I kept getting the error message 'Could not connect. Please try again.'
Comments
What is troubling is that this hasn't been fixed since beta 1 if you go by these posts.
http://nw-forum.perfectworld.com/showthread.php?50641-Bugs-from-Beta-Weekend-1&highlight=assault
http://nw-forum.perfectworld.com/showthread.php?44581-Dungeon-stuck-open&highlight=assault
And the thread for the suggested "fix". May or may not work.