Using forge version 2705 and the latest version of this mod (1.4.7), i found out that the small ceramic vessel has a bug where items will disappear from it if you move it in your inventory.
I tried by moving it by mouse or shift clicking and also by dropping it on the floor, but all methods result in the small ceramic vessel to be empty and the items to be gone without a trace.
Another interesting bug is that the small ceramic vessel can be stored in itself, which, well. It means it is gone after you close the window of course.