This.
The problem is that many people in the industry doesn't really understand the basics. How come is there a leak of your certificate, if that's the public key you're showing to every single client that connects to your SSL enabled site?
I've even seen sysads advising on forums about reissuing certs after Heartbleed, but no word about the keys.
Ugh. I think it would be better if revocation covered the public key instead of the serial number. (I'll ignore CRL bandwidth costs and the questionable usefulness of revocations.)
i.e. they re-used the same CSR without realising that the CSR references the old compromised key.
The odds of this being a real issue that will affect anyone are in the tiny fractions of a percent range.
You should not be responsible for website security if you don't understand the absolute basics of SSL certificates.
It would be helpful if the CA (or reseller) confirmed (dispay a warning) that you really want to reissue with the same private key and explain the implications of doing so.
When reissuing a certificate the default behaviour should be to revoke the old one after some specified time has elapsed - that is what reissuing is for and what distinguishes it from simply buying a new certificate.