Moving through wall bug (Sejuani, Gragas)

So, as in the MSI in FNatic vs SKT, everyone saw the Sejuani bug where she Q'd through the wall and was on the other side, yet it put her back on the other side of the wall.. I recently ran into this same problem while using Gragas.. I'm uncertain if this is for all champions that have an ability to move through a wall without flashing?