You guys can test it....I level with mostly PvP and my valor pretty much remains capped at my level. I'd like anyone to explain how I have had over a half a bar of valor into my next level IMMEDIATELY upon leveling.
I've made a point of checking my valor after leveling and have been far into the next valor level instantly. I've only tested this for a similar argument with guild mates who didn't think it was true either.
I'll try to catch it on my stream this week with one of my sub 50 characters that way it's recorded.
It's because the valor you receive from the match in which you level is already applied to the next level. But it's just the valor from that match. As you said you get out of a match and your valor bar is 1/2 full. If it was actually stacking you would get out of the match and it would be completely full, and when you dinged 50 you would see it jump up to like VL 54. It only takes like 3 matches to max valor level even at mid 40's, so it would make sense that as you leave the match you have 1/3 of your progress to the next level. Just as it also makes sense that if it only takes 3 matches to max valor, but 10 matches to go up a level you would have a LOT more saved up than just 1/3-1/2 of your next level if you in fact had 40 levels worth of stacking going on.