Wow, this thread certainly went from 0-100 in 2 seconds...
Seriously though, I've known about the limit for a long time, due to the fertilizer in my shoulder mount tames/dodos that I use for jamming that stuff into. 30 weight only usable.
When they are full though, you can't put a hat on, but take 1 out, put the hat on, then put the 1 back in and it works.
If we could find if it's a machine based limit, or whether it was made that way intentionally would be interesting. Hit one alpha on a boosted server, and you can't harvest anything more due to the amount of prime in your tame.