Sometimes it will ask for an item and, when I go back with the requested food, it has changed its mind and wants something else. I then have to buy this new food item to complete the Major Drills quest I'm on. I wondered if it had anything to do with timing but there's very little delay in buying a requested item and going back with it now that Major Drills has a link to the dragon.

I don't think this is a bug. The requested item changes every 5 minutes, so if you start the quest at, say, 9:59:30, you have only 30 seconds to give the item. It's the best to refresh the page at xx:00, xx:05, xx:10 etc. so you'll have the full 5 minutes to buy the item and hand it over.

Thanks.