Building the distribution kernel

Hi, I am trying to debug the problem shown in boo#1220524 - Files in virtualbox shared folder (on the guest) show wrong timestamp. Using the standard 6.6.5 default kernel in a TW guest (Xfce desktop) shows the problem. When I generate a 6.6.5 kernel starting with the mainline 6.5.0 and applying the patches in the kernel-source repo in the patches.kernel.org and patches.suse directories, the generated kernel works correctly! What am I missing? I am installing the kernel using 'make modules_install install', not from an rpm, but I do not expect that to cause a problem. Are there patches applied to the standard kernel that I am missing? Does installing from an rpm install other packages? Thanks, Larry