People have been claiming this forever about various domain registrars, and I just don't buy it. I think people play a logical trick on themselves, or succumb to paranoia, or similar. They are in the business of selling domains. That means volume is king. They want to move as many units as possible. The idea that they would 'steal' a domain from you right before you were about to pay them money for it is absurd. They…
AFAIK the practice hasn't been officially proven, but there's overwhelming amounts of anecdata pointing to this being real and endemic in the industry.