> It should turn bold but keep the asterisk displayed so you can still edit as normal.
This is just terrible UI, why do you need garbage marks when you already have bold? And you can edit "as normal" if you like, but that only requires displaying asterisks during that tiny % of time you edit the word, not all the time when you read it or edit something else.
So you can still see the actual text that you're editing. And to reduce ambiguity. If you don't leave them, then you can't distinguish between adding more bold text to currently bold text or adding non-bold text immediately after
This is just a personal preference. I strongly prefer to see the markup as I write it. I can't stand disappearing characters.