Notes 


Doing the math, a 2cm thick pot would only be 14.5cm in diameter and would only hold about 21 ounces of liquid (less than a pint and a half). If it were only 1 centimeter thick, it'd increase to 18.8cm in diameter and would hold 2/3 of a gallon, but getting a stone vessel that thin without breaking it could be difficult. 



By comparison, if we assume a barrel holds about 120 liters of liquid, the walls come out to being about 1.4cm thick (which isn't that unreasonable, given that equivalent modern barrels are 1cm thick). 



With the fix for 0004979, large pots now properly have a size of 5000 cubic centimeters (which makes them 5 times heavier than before), though their capacity of 60000 (presumably 60 liters) suggests that they still ought to be at least 34 times as heavy as they are now.
Doing some more math, a 100cm tall, 32cm diameter, 2cm thick hollow cylinder would hold almost exactly 60 liters of liquid and would itself be made up of almost exactly 20000 cubic centimeters of actual material. 



To...much...math... We could assume that barrels are thicker than pots are, or that uncanny dwarven magic that also turns the bones of a single kitten into shields, doors, and floodgates.
Either way I wouldn't consider this a bug as much as either an oversight or game logic at its finest. 
