[CLIENT] end of game screen will not pop up if system clock loses time by some unknown duration

my PC has a recurring problem where the system clock loses time every so often -- 15 minutes tends to be the minimum, and it sometimes loses over an hour. i have to manually go in and internet synchronize the clock multiple times a day to get it back on track.

if i am playing a game of league and my clock has gone back in time, the end of game screen will not load once i come out of the game.

as soon as i go in and synchronize the clock, the end of game screen immediately pops up.

it is not known whether there is a threshold of time loss to make this happen, or whether the time loss had to occur during any specific portion of the game play experience, or even if it is sufficient for the system clock to have lost time previous to the game play process beginning at all (i.e. "entering queue") -- the only known thing is that it is related to the clock being behind in some capacity when the end of game screen is meant to come up.

i am on windows 7 ultimate