Ok i "got it".
Pet summoned by a lock using :
http://www.wowhead.com/spell=115578 (Grimoire of Supremacy) is a "Minion" and not a pet or guardian.
The add-on just do not consider it at all being from the caster/owner which is why (seeing on the previous screenshot) it is listed as an additional damage source. (the "proc" imps which are guardians do show up)