Describe your suggestion:

Allow waterlogging of the Wet Mud Block, which makes sense since it has water in it.

Do you mean waterlogging of the wet mud, or dry mud into wet? I couldn't see either having many uses.

Wet mud is slightly shorter than a normal block, so I can understand the point of waterlogging.

Oh, why's it shorter?

I was thinking that it could actually be used in farms to hide water, since the block itself is slightly below the water block hieght.

And I believe it's shorter because it slows the player down when walked on.