vendors not showing stock

Hey I was trying to buy an item from a vendor (specifically Schematic: Delicate Arcanite Converter)
it says its sold by the engineering vendor in Winterspring but when I travel there and look at his stock it doesn't even show he sells it at all. also had the issue with buying Steaming Chicken Soup from the vendor in icecrown due to the same thing. bought some on my mage and was trying to buy some on my hunter and no option to even buy it.
anyone know what I'm doing wrong or is it just a bug on the server side?

You are trying to buy items that have restock timers due to them being rare. They re-appear every 8-24 hours depending from personal timers and settings

I retried after reading this and sure enough it worked. sat on the vendor for about 10-15 mins and sure enough when I re-clicked the vendor it showed the schematics in its inventory. Thanks alot I was dreading having to buy them for 200 gold from AH.