Interesting tip. I'm taking away the fact that I should transfer the nameservers away immediately after buying/transferring a domain (for Cloudfront, I presume?). Other than that, and ColdFusion hacks aside, my experience with them has also been fantastic.
So, when you point to new nameservers, anyone pointing to namecheap's dns during propagation will get SERVFAIL.
It sounds absurd... but I've gone back and forth with support about it, with no solution.