I'm not sure how you do it, but to avoid lag in game, I use LoL Recorder. It saves the info from the game without any disturbance to my actual game. I can then use that info to replay the game using the LoL Client, as well as navigate, change angle and look at different perspectives that I did when actually playing that game. It's then that I use a program to actually record the video feed.
Do you do the same thing, Adam? And if so, is there a hot key to turn off LoL Recorder? I gotta know to avoid that.