db after switchover ignores old level 0 and incremental image copy backups

 Hi! Does anybody know if following oracle rdbms behavior is correct:
There are two DB's - one primary and other physical standby db.
After graceful switchover an attempt to perform "rolling forward image copy backup" ignores (it tells that "no parent backup copy found") previously made level 0 and level 1 backups and performs new level 0 backup.
Backup is done to flash recovery area with nocatalog option, after switchover flash recovery area is manually re-cataloged on new primary.
Backup script I am using is simple:

RUN {
   crosscheck copy;
   crosscheck backup;
   delete expired copy;
   delete expired backup;
   allocate channel ch1 type disk;
   allocate channel ch2 type disk;