[Visual]Missing Champion health/resource bars

While playing the game, no champion health/resource bars were displayed. Tower, ward and minion health bars were still visible.

I am unsure how to reproduce this effect, but I suspect that it might have something to do with bad timing on alt+tabbing while the Champions are being "warped in". I have tried turning "Display health bars" under visuals off and on again, as well as shaking health bars. I also tried to disable and re-enable the "Display summoner name" option. None had any effect.

I attacked a screen shot were I was playing Malzahar, MF was an ally and Zed an enemy. Near an enemy turret with friendly minions and raptor camp visible.