There’s a mysterious issue affecting emulated switches under GNS3 through 3725s: incorrect static entries randomly
appear from time to time in the MAC address tables. This might affect proper operation of your topology.
A workaround is to clear the static entries of the MAC address tables on all switches whenever it is necessary with:
#clear mac-address-table static
This issue has been solved in GNS3 1.3.1; for HSRP cf. this thread, but not for VRRP/GLBP.