Items in Villager trade dissapear / math is wrong

I have a Villager trading hall with their workstations untouched in front of them. So far I have been able to make all the trades I want with no problems. However one trade seems to be doing something weird.

The Blacksmith, which you can trade iron ingots to emeralds specifically. In the Villager UI it says "4 iron ingots for 1 emerald", with a maximum of 6 trades per cycle. Fair enough. I have 2 stack of iron ingots from my iron farm and want to trade with my 4 blacksmiths. I give 24 ingots and visually it displays "40" after "64" in de UI. I get 6 emeralds. But when I take my remaining 40 ingots back, or exit the UI by pressing "E", there suddenly is only 22 ingots left from that stack. So 18 other ingots just dissapear while they are not traded. I do it again after the second trade which mathmatically then should leave me with 62 ingots, I replace the ingots in my inventory and it changes to 38 (now 24 missing?)

Either this is a visual bug not displaying the right cost of ingots to emerald, or the ingots are missing during the trade. See my short video to see for yourself. I dont know if maybe I did something wrong but so far this is only with this one trade. Has anyone else experienced the same thing in this version? (1.14.3!) Our multiplayer server doesnt update that frequently so this might be already resolved but Im not sure. I cannot recreate the bug in 1.14.4 (Singleplayer testworld) but the maximum trades did go to 12 instead of 6.

Thanks.