I’m not sure that Obsidian is alone is previewing emphasis incorrectly where the pairing is split in this way. See e.g. Markdown Live Preview.
I can’t find any reference but perhaps the markdown spec is unclear on what to do with these cases.
But it’s a simple enough workaround as your own example made clear. You manually insert underscores in place of single asterisks for the italics.
The GitHub link is, I think, a red herring since it refers to a different case, where a space intervenes before a closing bold (or italic).