http://www.tamingarchive.com/updates/000124.php
Currently on UOSA, pet loyalty drops one whole level on a failed command. I've tested this 13 times with a Wonderfully Happy pet - I command it at WH and if it disobeys I use Animal Lore and check it again, and 13 out of 13 times its loyalty was then Extremely Happy.Secondly, failed commands will drop a pets loyalty much faster now. A side effect of this seems to be that overall, it is much more difficult to control a dragon in the first place if your taming is low. I have heard reports that failed commands will drop a pets loyalty as much as one whole level.
Clearly from the quote, it appears that pre-1/24/00, pet loyalty did not drop a full level upon a failed command. I don't know what the *right* amount to drop was (or, possibly, the right percentage-of-a-chance-of-dropping), but it looks like in our period a failed command dropped by far less than one level.