Since 7.0.3 there is new functionality, that auto pop-ups quest dialogue from items, that start quests. That is pretty good but even if you decline, quest is accepted. Its minor annoyance with normal quests (need abandon quest if you dont wanna do it). And major one with Darkmoon trinket items (as described here http://us.battle.net/forums/en/wow/topic/20747795399)
This has been a thing with every auto-popup quest in existence. It show you the quest dialog, but you can't actually cancel it.
This is a new issue, in 7.0 items that start a quest will be auto-started by the game as long as you're level-appropriate to the item/quest.
This proves a problem in cases such as the darkmoon faire cards which when combined will auto-start the quest, deleting the deck by replacing it with a new item, making it impossible to sell.