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 (assuming hme1 is part of the same group). Removing hme1 from the group causes in.mpathd to move all the failover addresses back 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 it needs to be unplumbed, you should remove it from the group first, and then ensure that it has all the original IP addresses configured on it. 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.