WCF client can still connect after deleting service's certificate

I've got a WCF client and service. The service is configured to use a certificate for encryption. This is all working fine. We're using self-signed certificates for testing.

Except that one of my QA guys h开发者_开发问答as deleted the certificate from his client PC and he can still connect to the service.

I've looked in CERTMGR.MSC and I can't see any sign of the certificate anywhere on the client PC, either in his account or in Local Machine.

What am I missing? Where else should I look?

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We were looking in the wrong config file. He'd set certificateValidationMode="None". Bah.