I making some hardened leather from some time but i still have small amount of it. Now i know why...
I wandered why sometimes it disappears and thought that its just not 100% chance to make it.
I just read on wiki that hardened leather is used as normal leather in formulas. So if you craft more then one the next ones destroy previous.
I want to know i this was intended or bug.
IMHO hardened leather should be excluded in making hardened leather formula (only in this).