When I hit cmd+b, it starts bold, wrapping my cursor with two pairs of asterisks. If I’m done typing in bold, and I type cmd+b again, like I would in any other app in order to turn off bold, I’m wrapped in a new set of bold markup.
Perhaps this is a feature request: Can formatting like this be toggled? I imagine you’d just have to move the cursor to the right by the appropriate number of characters (in this case 2).