Similar looks to happen with bash: when I have a longer prompt and I resize the window to cause the prompt to line wrap, and I do that a couple of times, it starts looking like your screenshot. It doesn’t happen with dash. A difference between the two is that bash uses readline for line editing and dash doesn’t. If I run bash without using readline (bash --noediting) the issue does not happen.
I’m not familiar with zsh but I found it uses zle for line editing. I suggest disabling zle to see if you can still reproduce the issue then, just to point in a common direction why this happens with both zsh and bash.
I also note that this issue happens in other VTE based terminals such as the new Console app. I suspect the issue is between zsh/bash’s fancy line editors and VTE.