So I decided to turn some tokens into head tokens to get a cheese head from the food head villager, and when I click the trade on the left side of the UI for said head, all tokens go into the top slot, and when I try to take the cheese head out, or even put only one token in, I don't get the head, and my tokens get put back in my inventory. I didn't drop the tokens on the ground at all beforehand in case that breaks them and separating the 1 token from the stack of 6 broke the 2 stacks to not be stackable with each other anymore so I had a stack of 5 and an extra 1.

Here is a GIF of me interacting with the villager, trying to take the cheese heads out, to no avail. https://gyazo.com/ff0236663a5a58e982890499c9bb282f