Piston pushing magma block "boosted" water gets a WEIRD texture

When you push a water source from it's position over a magma block to another place underwater, there will be this (link: https://gg.gg/18w11a ) texture appearing for a millisecond, before then dissapearing. I have no clue why this texture got there and why it it aint the "original" "texture not found" texture :/
(i were unnable to attach the picture so you will have to use the link instead)
-CyBer00t