Last modified: 2013-05-24 18:54:59 UTC
When I tried to use the username I registered in wikitech.wikimedia.org (Ash_Crow), it didn't work and I had to replace the underscore with a space to be able to login on Gerrit.
AFAIK MediaWiki doesn't support underscores in usernames. It converts them to spaces.
You can use either in MW, it should be transparent. Reopening so I remember to look at this.