Question: why would fzy lines persist while fzf does not (in tintin++)?

[shmup]

This is me running a shell script from tintin++, a mud client (for the terminal). I noticed this behavior recently, and then tested fzf to see how it handles it. This does not happen when running these scripts directly from my shell. However, there being a difference in behavior for fzy and fzf makes me wonder what the difference in technique is.

fzf example Notice that when I cancel out (or if I selected something), there is no extra "lines" eaten up? I lack the words here heh

https://user-images.githubusercontent.com/118710/183779283-5c6031d0-f71d-401b-a223-bc8b99ee765b.mp4

fzy example Notice here that it keeps the lines used, which creates this gap.. again, I lack words lol

https://user-images.githubusercontent.com/118710/183779302-a3224b39-9cde-4f4a-850b-b42e6ca9f5a4.mp4

Any clue what exactly is the difference in technique, and furthermore, if this is something you'd be interested in tackling? Minimally, if you have any thoughts/ideas about the difference in behavior, maybe you could give me a little bit of detail.. Perhaps myself, or someone else in the future, would tackle it.