UOX3 version: UOX3 0.98-3.6f
Bug summary: When a player attacks a creature that the player himself owns, like a tamed pet or a summoned creature (like a bladspirit, daemon, fire elemental, etc.) he will become a criminal and turn grey for the duration of the timer set in UOX.INI.
In current UO it is not even possible to attack your own pet/summoned creature on the official shards, the only way to fight them is to tell them to attack you. I'm not sure if this was true for older versions of UO as well, but I'm pretty sure you didn't become a criminal for attacking your own pet.
To reproduce the bug:: Tame an animal, or summon any creature and then proceed to attack it.
To fix: Either disallow directly attacking tamed/controlled creatures (but allow defending against them if they attack you first), or disable becoming a criminal when attacking creatures you own.