In the Tremors of the Earth quest you click summon two dragons, kill them, and loot the chains binding them. Any time I've ever done it, they spawn at the same time and you have to deal with both of them.
Today while waiting for a couple lower level friends to help them with it, we watched two seperate groups summon the dragons one at a time. They approach the obolisk, one spawns. They kill it. They heal/drink whatever, approach the obolisk again and summon the second one. My friend after seeing this a second time went to the group and said "How are you doing that?" The guy responds "it's a quest." Umm.. yeah no kidding. My friend is patient though and asks, "When I do it you get both at the same time, how are you only getting one?" The response? "Hehe."
Unless someone can tell me otherwise I am going to assume these people are exploiting it and making it a LOT easier than it should be.
Dunno, might be bugged too. When our group did it we offered to help out couple of guys who were about to do it. They only got one and none of us, including them, could figure out why. Was rather frustrating since there was a long wait until the other could be summoned.
It's bugged. They could have figured out how to exploit the bug, but I kinda doubt it. To elaborate on what Koru said: First our group did it. We walked up, activated it, and both dragons spawned. Down they go. Now two other guys come up and would like to do it and they helped us a bit killing ours, so we stay and help them. They walk up, activate it, and....nothing. Nothing spawns. Nothing at all. Nothing. Needless to say this is rather annoying.
So we try it again using some leftover gems from our group. Again, nothing. So we try it yet again. Both of them spawn, but by my fault our group aggroed one and couldn't lose it. So we switch groupage around and try again. We spawn it again, only one dragon spawns, the one they got credit for already. Now we're out of gems, but as long as you have the Sign of Earth you can run around and recollect them. So two of us do it. We try again and the single dragon that they need spawns.