Folders created under a share with the names COM1,COM2,COM3, or COM4 are renamed when viewed from Windows. Examining the share's directory structure under Linux reveals no problem. The folders appear to have the names "CR23RR~9", "CR23RR-A", "CR23RR-B", and "CR23RR-4" for COM ports 1-4, respectively.
The Samba machine is running Fedora Core release 6 (Zod), but the bug doesn't appear to occur until the folders in the Samba share are viewed from Windows. All the directories look fine in Linux.
The following site is the only other reference I've found to this issue. However, the site is in Russian and Google's translation isn't very good. I can't determine if they found a solution.