I thought the core was completely different during 4.0.6.
At that time some dungeons were working and were working quite well, Scarlet Monastery for example, also there was Hellfire Rampants. So the 4.3.4 messed those up? Those dungeons along with most of them have been closed for some time now.
PS:
The only issue, which was minor with Scarlet Monastery during Cata were these:
1. If you 1-shot Moragrane, can't remember his name, he will not be revived to fight again, so you will need to restart, but it worked fine if you don't 1-shot him.
2. The boss in the SM Library only walks around before fighting him, he was suppose to just stand there, but the fight worked well.
3. An extremely light fix was the use of SM keys to open doors to other instances.
TBH, I didn't see why those dungeons were closed, they worked fine, this is coming from someone who runs players for a living in-game instead of going all out end-game gear and such.
At the time, those dungeons worked in cata, no bugs, no nothing, the only one that didn't work was ICC and so on. Most players were too busy in from of Stormwind/Orgrimmar to even realize this, glad I was a Dungeon Dweller at the time before closing xD.

