Cannot step into System.Security.Cryptography.X509Certificates methods

Question

I am trying to debug .net framework code for working with certificates. Code example:

X509Store store = new X509Store(storeName, storeLocation);
store.Certificates.Find(findType, findValue, false);
and
(RSACryptoServiceProvider)signerCertificate.PrivateKey;

VS has loaded all available symbols from MS symbol servers. It does step into other .net framework code.

Debug Modules window shows that only security module that is available is System.Security.ni.dll, and status is "Cannot find or open the PDB file."

Is this due to .net framework version (4.5) or are Cryptography debug symbols generally not available? Are they available on some other location?