In Burning Crusader Classic, The Attack! quest in stormwind requires your quest log to be at 19 or less even when the max is now 25. I was at 22/25 quests and had to abandon 3 quests when my wife started it in order to accept it.
I also just experienced this with the escort quest Rescue from Jaedenar. Had to be at 18 in order to accept the quest even though the cap has risen.