Caesar is calculating elemental loads the only way it can, by considering everything you tell it that acts between nodes. Fluid weight in a vertical line is always a tricky one, since Caesar (and every similar software package) cannot know that the fluid weight alone acts elsewhere.
The same applies to, for example, a vertical line onto a pump nozzle where the fluid weight acts on the pump casing and not on the nozzle flange.
You can easily modify your model to accommodate this, but you should also be aware of it.