I just joined a CT run in progress and noticed there were only a few people in, thought it was curious and began to run to the first room of mobs only to notice the walls were up as if someone was battling it, but this was not the case.

The instance is bugged and because there is people joining/leaving it is the only instance for the "Join in Progress" option, so for the next 90+ minutes or w/e is left on it the instance is broken and therefore "Join in Progress" is broken as it will always join this instance.

Screenshot: http://i.imgur.com/pgzbBfG.jpg

Time: 28th Dec 2013 - 21:50 GMT+0
Frequency: For the duration of that instance, all the time
World name: Excalibur / Duty Finder
Character name: Meow Rawr
NPC name: n/a
Monster name: n/a
Class/Level: n/a
Party or solo: Solo
In-game time: All times
Area and coordinates: Crystal Tower
Steps:
1. Tick join in progress for Crystal Tower
2. Instance broken, first room is closed