Yeah, this is a stupid bug I decided to introduce... Whoops! Anyways, have found and fixed the problem, so won't happen again once we update. Doh. I'm hanging my head in shame though.
Valor xp from PvP Battlegrounds is determined from the Valor medals accumulated during the game. 25 valor xp / medal is the current conversion rate.
Though, looks like there's a bug in this system on the live server with any Valor medals held being lost when killed. (It'll be fixed in the next build we push). But to clear up any questions about the valor medals in PvP Battlegrounds, each scenario (Deathmatch, Capture the Flag, Domination) have slightly different rules for obtaining valor medals.
In Deathmatch you are awarded a medal for reaching 10 kills, 25 kills, 10 assists, 25 assists, obtaining a score of 500 or more and surviving for 5 minutes without a death.
Capture the Flag awards medals for capturing a flag, capturing 3 flags, 5 flag denies, 10 flag denies, obtaining a score of 150 and surviving for 5 minutes without a death.
In Domination, Valor medals are given for capturing a point, capturing 3 points, defending 5 points, defending 10 points, obtaining a score of 150 and surviving for 5 minutes without a death.