Some final code requests (and screenshots)

The Random spell (Pearl) it cast has nothing to do with it doing a critical hit, unless I'm misunderstanding the question, what I think you're referring to is the 'extra effect' flag that's set on it and a couple other weapons that takes some MP to do a for sure critical hit. If that is what you mean, that can be taken off in the FF3usME equipment editor (Reg. Items (adv.) under the 'Extra effect' (Uses MP for mortal blow).

Nope, I'm not referring to the MP criticals dealt by the sword itself, but rather the random Pearl that deals double the normal damage to monsters. For example, I just now used the Illumina on a monster in the WOR and watched a random pearl cause 3,500 damage.  I then casted pearl manually using the magic menu on the same monster and only did 1,900 damage.  I always thought this was a bug, because Flare does not do double damage with the Ragnarok, nor does any other spell with any other sword. I was always under the impression it was because the critical hit caused by the sword was carrying over to the spell, making it a "critical hit" with a spell.  I would be surprised if nobody has ever looked in to this!

Edit: It does appear to be linked to the MP criticals of the sword. If the attacker doesn't have enough MP to perform a MP critical, then the random Pearl casted by Illumina will do normal damage. If the attacker has enough MP and the sword does the auto-critical, then Pearl does twice as much damage if randomly casted. I am pretty sure this was an oversight in the original game, and would be shocked if it were not a bug.