Repro steps: You want to type bold text, so you set boldface with Ctrl-B. The editor inputs
**strong text**, all selected. If you immediately begin to type your text, the selection will disappear and your asterisks will be gone, leaving your text un-bolded. Currently you must re-select the words before typing. Minor annoyance but there it is.
It’d work better to only select the words, and not the surrounding asterisks. Alternatively, you could omit the words and place the cursor between four asterisks. I’ve seen Markdown editors do it both ways.