All newly created clients will get an entry in the client section Index=n where n is the number of the IPBIND_n. If the same client tries to acquire a new IP address but from a different IPBIND_k interface then the software will recognize that n != k meaning the client section is created from a different IPBIND. In that situation and when DeleteClientsFromWrongIndex is 1, then DHCP server will delete the client entry and create a new one. Please keep in mind that this will work only, when the client section includes the Index=n entry which is only the case after the client has been acquiring a new lease.
[Settings] DeleteClientsFromWrongIndex=1 ; Default: 0
This feature was an added in V2.6.0.