Dangerous Love

I just spoke to a GM who confirmed this will be fixed on Tuesday's restart.

http://eu.battle.net/wow/en/forum/topic/1679478190

Q: I’m having issues with the vendors – apparently I can’t buy what I want because ‘You can’t buy the specified quantity of that item’. Help!

A: We’re aware that there seem to currently be some issues with attempting to purchase the items bought in stacks already, but in the meantime you should be able to get around the error message by making use of the /run BuyMerchantItem() script.
Here are the appropriate values for all the affected items;

Lovely Rose ► /run BuyMerchantItem(2)
"Bravado" Cologne ► /run BuyMerchantItem(3)
"STARWART" Cologne ► /run BuyMerchantItem(4)
"Wizardry" Cologne ► /run BuyMerchantItem(5)
"VICTORY" Perfume ► /run BuyMerchantItem(6)
"Forever" Perfume ► /run BuyMerchantItem(7)
"Enchantress" Perfume ► /run BuyMerchantItem(8)
Handful of Rose Petals ► /run BuyMerchantItem(11)
Love Rocket ► /run BuyMerchantItem(12)
Silver Shafted Arrow ► /run BuyMerchantItem(13)

Nearest and Dearest

Complete the questline starting with Dangerous Love (Horde) or Dangerous Love (Alliance). At the last quest, make sure you click the cauldron!