[Gameplay] Incorrect Cooldown Displays

In the time since Patch 5.03, I've had a strange but rather debilitating bug (in all games, across all queues and modes) wherein all of my cooldowns appear to display wrong by about 10%. The timers count down normally, but after the timers visually expire, it is still several seconds before the spells can actually be cast. It's most egregious on summoner spells and long-cooldown ultimates, but it appears to apply to all spells.

I have not yet encountered anyone else with this bug, but it has resulted in my death several times.