Can't turn off mercenary mode?

I've unticked the option in account settings but I still keep getting put in opposite faction?

If you’re on Blackrock, you can’t always choose to turn it off, if there aren’t many people in the queue, it will be forced to be enabled.
On Icecrown, you can turn it off and it won’t be forced.
(I’m not sure about Lordaeron, but I believe it works the same as Icecrown.)
If you are not on blackrock realm , once you login the game Queue Random battleground then right click the mini-map battleground's icon and confirm it is disabled.

Try disabling it from the site when you are not logged into the game, or try disabling this feature before queuing for bgs.