Bug Item that will disappear into exchange mail chest

[Akamith]

Couldn't find anything on forum about this so
Was buying things in exchange and then I tried to open mail chest but nothing was loading when I pressed dispenser item at bottem
Then I accidently pressed my spade and it disappeared while the mail menu was still loading sat and waited for it to load my mail and it never came back after load finished
I heard about this happening but cant find anything on forums about it, Is it still counted as a bug if its lag related?

 

[WitchOnaRampage]

I'm not sure about a dispenser - did you click on the redstone repeater? This changes the view from items for sale to items bought I think - clicking on the repeater often makes bought items appear.