Hello,
I was able to duplicate water by stacking water jugs or water bottles. If I use two empty containers and fill these stacked items, both are filled, however, the quantity is not divided but duplicated. An easy way to avoid this is not allow stacking these items but maybe there is another solution though I do not mind this anyways just wanted to inform you. Here is an image in case you want to replicate this issue:

So you are saying you stacked 2 empty containers and you filled them while they were stacked.
And then when they split there were both full.
Technically this is intended behavior.

Merged post

If you would like this to not be intended behavior I can look into adding an additional check. 
However, since you have to fill the containers anyway it doesn't make much sense to fix it in my opinion.