We are in 11gR2.
For incremental level 1 backups (differential) followed by a RMAN Duplicate command, it has been observed that
RMAN ignores the last incremental backup performed, which in turn can cause that you will loose some data in your recently duplicated DB.
We have found a workaround for this behavior, by issuing a "alter system checkpoint" at the end of the backup script.
Oracle documents a bug only for the cumulative backups, with expected resolution in version 12c.
Rman Duplicate Does Not Use The Most Recent Incremental Backup [ID 1195673.1]