User A has given read permissions on his/her Agenda in GroupWise to User B. After the migration with ACL and proxy right migrated, you see that User B has "send-on-behalf' permissions on the mailbox of User A.
User B was not able to send on behalf of User A in GroupWise.
This is by design. Users listed on the Proxy tab in GroupWise will be set with “send-on-behalf-of” in the target.
Disable ACLs migration with the following parameter: