I’m not sure if I’d call it a bug, it has always behaved this way. It’s more of an undesirable behavior at times.
It’s also worth noting that you were using a similar trick but using par inside each item’s body (not the items themselves) instead of block, basically. That’s why it doesn’t work now (the list item bodies no longer are paragraphs unless you add parbreaks), and also why show list.item is undesirable as it applies to each bullet point + body.