So I've investigated this issue, and while Moo Fluids is probably doing something less than ideal (picking fluid too early, on entity construction, rather than on spawning), this is fundamentally caused by TheOneProbe. It's creating a new entity every frame that the probe is displaying information about an entity. By the time Moo Fluids has set the fluid type correctly on the displayed entity, TheOneProbe is already creating a new one with a random fluid. Even if the behavior in Moo Fluids was corrected, TheOneProbe would probably either display the cow with no fluid, or it would flicker between none and the correct one.
So I've investigated this issue, and while Moo Fluids is probably doing something less than ideal (picking fluid too early, on entity construction, rather than on spawning), this is fundamentally caused by TheOneProbe. It's creating a new entity every frame that the probe is displaying information about an entity. By the time Moo Fluids has set the fluid type correctly on the displayed entity, TheOneProbe is already creating a new one with a random fluid. Even if the behavior in Moo Fluids was corrected, TheOneProbe would probably either display the cow with no fluid, or it would flicker between none and the correct one.