I am using Kandarim client, just updated.
Copper pot fills up to 5l when is empty and filled from a full bucket. Second click makes it 10l. This can be considered a feature, when you need to fill it partially for whatever reasons. Funny I did not notice that until you wrote about it.
I am referring to the bug in the level bar itself. It has nothing to do with double right clicking. No matter how the bucket is filled the percentage is calculated in regards to 5l base instead of 10l when the pot is on a fireplace. When it is in the inventory amount of water is correct and moving water to and from a bucket works fine.
That makes me think that somewhere in the code there is still 5 instead of 10.

- pot 1.jpg (31.4 KiB) Viewed 1656 times

- pot 2.jpg (16.76 KiB) Viewed 1656 times
After filling to 10l:

- pot 4.jpg (23 KiB) Viewed 1656 times