Hello,
This is strange. The virtual MAC address of a HSRP/GLBP group should be stable and should not change if the active router changes.
Please provide us with the following information:
1.) The virtual MAC addresses of the HSRP/GLBP group as created by your 6500 and 4500 routers.
2.) If possible, the configuration of the interface where the standby group is being run.
Best regards,
Peter