I had at several occasions in which I tried to register an expired domain name, got an order confirmation email, only to find out that someone else registered the same domain a few days after I tried. I thought maybe they were isolated incidents, bugs. Last week I registered a domain that a client let expire, we breathed a sigh of relief. Several days later, another company had ownership of it. The clueless tech support at the host company couldn't offer a real explanation of why my registration didn't go through, and how someone else managed to acquire it DAYS after I tried.
In short, if a domain is valuable, stick to the main two or three domain registrars, and do NOT go through a company known primarily for hosting. You probably won't get the domain, and their support staff are utterly useless when you confront them about it.