Just found a bug: when you put a bucket of Tar into the tank of the an adventure backpack, the GUI will desync. And if you taking back the Tar from the tank, it will come back to normal.

P.S: Is it normal that i can collect Tar with a normal bucket?

Tar uses forge's fluid system, so this is a problem on the adventure backpack side. And yes, you should be able to use a vanilla bucket.

Okay then.