Julia Gilmore About:

We do like having Markdown as the default editor (it's been requested by our IT staff).

Note that there are several known issues with Markdown support, see https://jira.xwiki.org/issues/?jql=project%20%3D%20MARKDOWN%20AND%20resolution%20%3D%20Unresolved%20ORDER%20BY%20priority%20DESC%2C%20updated%20DESC

ATM you'll get better rendering using the XWiki Syntax.