Possible McAfee GroupShield Vulnerability

I have found a possible GroupShield vulnerability involving protected Windows operating system files with a .sys extension.  I am currently blocking by extension and it is allowing the files to come through successfully our Exchange server system from the outside.  I have been working closely with McAfee on this issue, however they appear to be content in ignoring the bug.  I was wondering if anyone out there would be able to write a malicious POC file that would be able to slip through the GroupShield product based on these principles.  Successful files sent include msdos.sys, config.sys, and pagefile,sys.  Mcafee claims that it is a 0 byte issue (file not registering any size are allowed) however I am able to successfully modify these files and send them.  I am a network administrator and not a security expert, so any help would be appreciated.