What the Deserter is
"The idea that players would have to remain in battlegrounds for ten minutes before they'd receive a Mark of Honor for losing was one the developers were seriously considering as an effort to reduce the incentive players had to lose a battle quickly. The concept was simple: it would give players incentive to try and stay in, rather than giving up and allowing a quick loss without any effort expended. However, during further discussions, it was decided that adding a mild punishment to those who /afk out of battlegrounds, in the form of a requeue timer (Deserter debuff), would be preferable to the old "ten-minute rule" idea."
http://wowvault.ign.com/fullstory.php?id=13250
To Leave a Battleground without the Deserter debuff
1. Logout
2. Login
3. Type /afk to leave to Battleground
I found this unintentially when working with macros inside Warsong Gulch and I can't really say why this works.