When you execute the ifconfig command's group parameter with a null string, the interface is removed from the existing group. See How to Remove an Interface From a Group. Be careful when removing interfaces from a group. If some other interface in the multipathing group failed, a failover could have happened earlier. For example, if hme0 failed previously, all addresses are failed over to hme1, if hme1 is part of the same group. The removal of hme1 from the group causes in.mpathd to return all the failover addresses to some other interface in the group. If no other interfaces are functioning in the group, failover might not restore all the network accesses.
Similarly, when an interface is part of the group and the interface needs to be unplumbed, you should remove the interface from the group first. Then, ensure that the interface has all the original IP addresses configured on the interface. The in.mpathd daemon tries to restore the original configuration of an interface that is removed from the group. You need to ensure that the configuration is restored before unplumbing the interface. Refer to Multipathing Daemon to see how interfaces look before and after a failover.