I've stumbled across MC-249486 when seeing if somebody else has reported the fact that there's no waterlogged texture for leaves in Fast graphics. Developer Moesh commented that it's intended because you can still see the particles beneath. However, after testing, it seems that when a leaf block is waterlogged, it very infrequently (once every 30 seconds or so) produces a light blue particle underneath.

The issue can be fixed by making the particles spawn more frequently, and on top of the leaf block as well.

My particles are set to All and I am not using any resource packs that should affect anything.