How does water AI/pathfinding work with this?

[AechtRob]

I own the Prehistoric Nature mod, which adds a lot of water content. Our mobs seem to not be able to move any more when in a waterlogged block (eg. on a top of a slab under water). How does the Fluidlogged API actually work? If I don't implement the API in code but just install the mod. I am looking for some info about what this means in terms of the java MoveHelpers, Navigators and Pathfinders and AI for aquatic mobs and movement. I'm not clear whether the issue is AI (find a target or Material Type Water) or a Navigator (find a path) issue. Are waterlogged blocks re-categorised as the vanilla Water Material? Does it do other stuff, etc.?