So, I've been farming for a PYEC for a couple of months now. Long story short: today I got it!!!

But I only noticed I got it at the end of the day when I was looking through my "session results" pane for something else, and noticed "Platinum Yendorian Express Card (no-sell) (1)" in there. Strange, I thought, I didn't fight the MoT, or mafia would have stopped for me. Grepped through my log, and found this:

[65254] The Dungeons of Doom
Encounter: ELDRITCH HORROR Master Of Thieves
Round 0: Xande1 loses initiative!
Round 1: Xande1 executes a macro!
...etc.

So my best guess (not having time to dig through the code) is that the intergnat's name modification is what caused mafia to not notice I was fighting him. It doesn't matter to me, because I was level 256 at the time, and even when I'm not, I have enough shinies in my CCS that even in run, I'd be very surprised to lose against a UR. But I know the mafia team is pretty serious about stopping on UR's, so I thought I'd come over here and let y'all know what happened.

And yay for URs!