why does my battleground log in for the second faction?

why does my battleground log in for the second faction?
I'm a gnom at the alliance and I log in to battlegrounds as an undead to the horde. Why?

turn off traitor mode-mercenary mode.

https://www.warmane.com/account/settings
Remove "Opt-in Mercenary Mode"

You can read about mercenary mode here: http://forum.warmane.com/showthread.php?t=399487