The split() block’s top left shading is acting kind of weird when I hover another block over it.
You don’t have to fix it, it’s just something weird I found.
You are talking about the first input slot being highlighted with the white semitransparent oval?
There is hidden a Shift 
\red{\text{Prefer empty slot drop}} that blocks replacing the occupied slot.
No, I’m talking about how the top left corner shading of the split() reporter is disappearing when I hover the keep items reporter over it.
It’s kind of hard to spot, so I would recommend opening the GIF in a new tab and zooming in.
Indeed…
Chrome@Win10, 2560x1440 no sign of distortion.
This highly visible dithering on your screenshot is a compression artifact or just very low color count of your display?
Its a GIF, and the GIF form of compression is just losing certain colors
This is actually the same bug I reported here, with the exact symptom described in this post being discovered previously here:
What is going on is, when moving down or to the right with an object (window, block, etc), the input slot’s bevel get’s drawn in places it shouldn’t (on top of other block’s/windows and slightly outside of the area the bevel should be). In your case, the ring’s interior hole has a bevel which is getting “spread around” and “smudged” so to speak when you move objects over top of it.
I’m on Chrome and Windows 11, and
Damn…
Alright, I’ll try that when I’m on my computer.