Pasting bullet points inside bullet lists often breaks hierarchy, but more importantly, it also flattens existing bullets, which is data loss.
You can see an example here (video). At the end of paste, children of C end up being peers to C, even though they didn’t start as such.
I encounter this all the time and it makes keeping lists in Bear tricky. It seriously bit me just right now, because it flattened some hierarchy on some paste a few hours ago, but I didn’t notice – and now I have a long list that’s flatter and really confusing as a result; I had to spend a bunch of time restoring it by hand, because relevant undo was too far away.