I ran into a list-rendering-related inconsistency in ProseMirror. After digging around, I found #51 (TIL about "list tightness" in Markdown!), and the fix does seem to correctly detect the "hidden" attributes in Markdown-it's tokens and correctly attaches them on lists, but the then the (default) list rendering does not take these into account:

In the above screenshot, the left-hand side is plain Markdown-it, the right-hand side is ProseMirror. As evidenced by the data-tight="true" in the list DOM, the tightness is correctly detected but ignored on render.
This behavior can also be reproduced by the Friendly Markdown example on the website.
I tried looking into where this gets rendered (is it prosemirror-schema-list?) but arguably I'm still a bit new to ProseMirror's internals and couldn't quite get to it, would be happy to help to have this fixed.