I have a friend that races his Moots YBB like that, with the stem inverted.
It looks silly to me but he swears that it just feels better to him when he races. The frame is his size but he just likes to be a little more "hunched" over the bike. Maybe it's because he is more a roadie then a dirt guy.
I remember when Cannondale racers BITD first started racing the Headshock frames they would do the same thing. Always puzzled me.
To each their own I guess.
1968 Schwinn Typhoon Deluxe
1984 Otis Guy
1990 Klein Rascal-Owned by Steve Miller
1990 Klein Attitude XT
2010 SSCXWC Raliegh Cross
2012 Black Cat Custom 29er SS