Numerous bugs when shift+clicking in Wandering Trader UI

It's difficult to describe what's going on here. Sometimes the output switches to something else, sometimes it gives you more items then it should, sometimes it gives you emeralds back, at one point I was able to shift+click and get the items without spending any emeralds but I haven't been able to recreate this.

I attempted to record a video of these things happening but trying to show them all made the video too large to upload, even after cutting the less important parts out. If the video would be helpful I still have the file.