Moddable but un-sellable and un-keepable Patriot??

So, ran into something really strange today, and I can't find any info on it. Hoping someone else knows something or has seen similar.

Today while I was doing a Gang Attack, I cleared it out and found a Mammoth Patriot in the zone. It was a Simeon vehicle, so I figured I'd pick it up and grab some quick cash.

Well, first thing I noticed odd is that it didn't pop up with my immediate two-stars and tell me to lose the cops. (I was being chased by cops already at a 1-star level, thought that maybe interefered with it.)

So, that was a little odd, and I thought maybe the Patriot was a special mod vehicle, so I wanted to keep it. Took it to the garage, got told that I couldn't store it.

Okay, even more bizarre, but at the very least, I should try to take it to LSC. So, you'd think it wouldn't even let me in, right? Well, wrong. They let me in the door, did a repair on the vehicle, and saw that I had a bunch of customizations open for it. But... I couldn't sell it. That option was missing.

So, I have no idea what's going on. I've never seen a vehicle that you can mod but can't sell/keep, and the game seems to treat it like a special vehicle, even though it just looks like a normal Patriot. The only weird thing is where I found it, which was in a Gang Attack that seemed to be some kind of para-military force. It looks completely normal though, so I have no idea.

EDIT: Ask a question about something I thought was odd, get downvoted. Stay classy, Reddit.