I suspect that the problem may lie in the mount.cifs command to mount the samba server. I also am having the same problem access my samba shares on my FC5 file server from my FC6 box. No problem accessing and viewing the same shares on my Win2k box, just from my FC6 box. Like you, my mount statement calls for a CIFS connection although I use specific users and passwords embedded in the mount command.
I did file a bugzilla report today: https://bugzilla.redhat.com/bugzilla....cgi?id=214735
I hope to get some answers as I run a mixed network, so I can't just server the files over NFS. I believe it only happens with large sub-directories. I can view many sub-directories, but it chokes on the large ones.