Pool Party Fiora Waist Deep on Fountain and Feet deep on rift

I've seen this happen on multiple pro streams with different champions. Not sure what the cause is.

Edit: I think it started after the patch where they made adjustments to how particles that overlap terrain are displayed, so that the abilities wouldn't cut off at map intersections.

Looks to me like a teaser for the summer Summoners Rift.

The whole rift will be a big pool, and So character models will be partially sunk in.

They are merely testing the code for sinking the characters slightly. Mark my words.