Items disapearing from furnance

After i mined 3 stacks of iron i put them in the furnaces after that i went to farm some exp. When i returned my iron was gone, aswell as the buckets i put there.  This keeps happening to me, and this already happened to me multiple times  this day. Some weird things about this:

After items in the furnace disapear fire never goes off, despite nothing being there.

I did a few tests and this happened to me when i was (around) 1000,300 and 50 blocks from the furnace, but this doesnt happen when im very close to the furnace.