I'm getting seemingly infinite add spawns in 25man p1 as well... how many did you have to kill exactly? Since you didn't attempt this solo, for all we know, the mechanics are different when you're on your own.
Edit: Double-checked, Sara gets stuck at 1HP and just won't die.
[BUG] SARA:PHASE 1 ULDUAR 25 PLAYER [BUG] - Forums - World of Warcraft Other people are also reporting this bug, but since this guy was in a party when it happened, I doubt the bug is tied to doing this solo. No idea what triggers it or why.