Valor flag the next "priests"
Basically when valor flag is taken it resets the opponents troops to their base hp, regardless of their possesion of another valor flag. So when you take your opponents flag for the first time, and they retake it back - you lose the bonus of your own valor flag.
Now I find myself telling my teammates not to capture it just as I was asking them not to get priests. It is not as game breaking as priests were, because it happens a lot later in the game usually and grunts have much less impact at that point of time, but it's a nasty bug none the less. Also losing 30% hp (and very likely damage) bonus to your grunts in a situation where you have Giants and Catas is nothing to sneeze at.
I guess when you first take valor flag it becomes imperative to keep it locked non stop.