Miscount of trading items while trading and replenishing slot

Summary: MC loses count of the number of items I have while I am trading if the first slot is not full. It seems to restore the original contents of the second slot even when I've traded them out.

It's a bit difficult to explain so please watch the short video! But I've tried to summarise the key steps below.

This happened in multiplayer (not the host) but I've seen something similar in single player. When I went to capture the screen (ie paused interacting), it would resolve itself so perhaps that's relevant

I am holding raw flesh. The first two figures are the inventory slots, the third is the active trading one and the fourth is the total in brackets.

17 + 61 + 27 (105)

I fill the slot from the one holding 61. Briefly, the slots then show

24 + 17 + 64 (105)

but almost instantly the numbers jump to restore the original value for the second slot.

17 + 61 + 64 (142)

then one moves because I'm still holding the button

18 + 60 + 64 (142)

I trade for one emerald.

Then I transfer again

23 + 18 + 64 plus one mid-move to the full trading slot (which should fail)

Then as that one moves back to first slot,

19 + 59 + 64 (142)

I trade again for an emerald so I now have

19 + 59 + 27 (105)

For an instant I have

22 + 19 + 64

but it jumps to

19 + 59 + 64

I have also seen this where only the first slot of my inventory is in use (eg I am holding 62, I transfer to fill the trading slot leaving about 25, then the total for that jumps back to 62).

This continues until the villager stops trading the flesh. I have not seen it with other trades (but haven't done that many).