This configuration is working for me. Perhaps nginx cannot verify the OCSP response with the bundle in /etc/pki/tls/certs/ca-bundle.trust.crt ? In my ssl_trusted_certificate file, I have these certificates, in order.

C=US, O=The Go Daddy Group, Inc., OU=Go Daddy Class 2 Certification Authority
C=US, ST=Arizona, L=Scottsdale, O=GoDaddy.com, Inc., OU=http://certificates.godaddy.com/repository, CN=Go Daddy Secure Certification Authority/serialNumber=07969287

I put my file in http://pastebin.com/G10e4sRh for reference.
Hope this helps!

Ryanne