Bug in Quests Requiring NPC to Travel

I've noticed a trend in the quests I've had to abandon. I didn't notice until I accepted Deepholm, Realm of Earth. When Thrall tells me to talk to Aggra to ride her Wyvern, I'm not given the option to ride it, so I'm stuck. Sane thing happened when I had to talk to the lady at star's rest to teleport to Dalaran and when I had to talk to a dude in Dalaran to get to Icecrown. I'm not given an option to get a ride over. I got around it both times before but this issue is more difficult to sidestep.

Same thing with Call of Duty just now. The exact problem is that the game is wrongly saying I completed my ride as soon as I accept the quest, which keeps me from being able to do it.

Any ideas how to complete Call of Duty?