I sent an e-mail to the camera shop after fielding comments from here, Rangefinder Forum, and the Zorki Flickr group. They sent back an email explaining that there wasn't any risk in changing the shutter speeds—which is correct for this camera. I responded by explaining if it were the model with the slow speeds, they might have busted it (and the underlings didn't know there was a difference in the first place). Best case scenario, they didn't know what speeds they were testing, so I didn't even know what they were testing.
The shop owner responded: "I'll make sure they test by changing the shutter speeds first from now on—there's no extra effort in doing it, so we might as well." He asked me to bring the camera in so he could test it himself. When he did, he got stable enough shutter speeds for his taste (he thought the 1/500 was going too fast until I told him there was a mystery 1/1000 right next to it).
He did tell me, however, that the shutter curtains are timed so that there is uneven exposure across the frame by ±1/3rd of a stop. He said it's probably something that cannot be adjusted out (changing it at one speed would make the problem worse on other speeds), and it shouldn't show up too much in pictures.
I emailed Yuri at Fedka.com, and he said he agrees: that's about as good as it gets. I'm inclined to agree, but I don't know squat about cameras.
What do you guys think? (;