Water will spread onto glass pane corners like they are air, flooding the other side of the glass. This makes it impossible to have a glass pane room underwater.
I DID NOT MANUALLY PUT WATER ONTO THE GLASS PANE TILES. LOOK AT WHAT I AM DOING IN THE SCREENSHOTS. IF YOU MARK THIS AS A DUPLICATE OF 127237 I WILL ATTACK YOU WITH LARGE POINTED STICKS.
Duplicate of MC-130203, a source can be created in that situation, thus it will be waterlogged.