Colored rectangles appearing over minions, towers, nexus etc.

I keep having the bug seen in the screenshot attached intermittently in game. Red and Blue rectangles appear for enemies and allied units respectively. Have not seen any on jungle creep to this date. Also affected that I have seen are turrets, inhibs and the nexus, again both allied and enemy. This did not happen prior to patch 4.20, and I had played many games on the new Summoners Rift (beta) prior to it.