I've seen this, too, and was quite confused until I realized what was going on. It's not site-breaking for me, but I do find it odd.
It probably happens because in this case, the child comment is the "center" of the comment tree, and the dev may have wanted to present it's parent as a tree going the opposite direction. But it is confusing.
I must be in the minority here in thinking that this is virtually site-breaking. Whatever broke this should have been rolled back immediately.
I logged in after a few days to about 20 replies and had no easy way to tell what comment of mine people were replying to. I gave up searching after a while.