ok im pretty sure this time its actually broken and not a temporary feature
ive now tanned at least three rounds of leather using large hides in the same tanning tubs and the fluid meters appear to be frozen where they are
if i had to guess i would say it's been going on since the animash patch that "fixed" the required fluid for large hides but im not 100% sure on that
e: due to grumpypants nerds this is also a formal suggestion to make tanning fluid less EXTREMELY ANNOYING!!!!!!!!!!! to make