Bond, round robin mis-configuration.

Hi, In the kernel 2.6.39.3 ( /drivers/net/bond/bond_main.c). In the function  ‘bond_xmit_roundrobin’ The code check if the bond is active via ‘bond_is_active_slave(slave)’ Function call. Which actually checks if the slave is backup or active What is the meaning of slave being backup in round robin mode? Correct me if I wrong but in round robin every slave should send a packet, regardless of being active or backup. Thank you,             Eduard