Strange RMAN snapshot controlfile issue

A strange thing happen today. I executed a delete obsolete command on my RMAN prompt and it reported the snapshot controlfile as obsolete. I don't know under which circumstances this problem occurs and I couldn't find any relevant information on forums or metalink (oh! sorry "my oracle support") about this.

Below is the output of the DELETE OBSOLETE command:

RMAN> delete obsolete;

RMAN retention policy will be applied to the command
RMAN retention policy is set to redundancy 1
using channel ORA_DISK_1
using channel ORA_DISK_2
Deleting the following obsolete backups and copies:
Type                 Key    Completion Time    Filename/Handle
-------------------- ------ ------------------ --------------------
Control File Copy     36     29-11-2009 12:35:33 /u01/app/oracle/product/11.2.0/
                                                 dbhome_1/dbs/snapcf_tetris.f

Do you really want to delete the above objects (enter YES or NO)? y
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03009: failure of delete command on ORA_DISK_2 channel at 11/29/2009 21:11:16
ORA-19606: Cannot copy or restore to snapshot control file

Indeed, this is the default configured snapshot controlfile:

RMAN> show snapshot controlfile name;               

RMAN configuration parameters for database with db_unique_name TETRIS are:
CONFIGURE SNAPSHOT CONTROLFILE NAME TO '/u01/app/oracle/product/11.2.0/
dbhome_1/dbs/snapcf_tetris.f';

It seems I'm in a kind of deadlock here. The snapshot controlfile is reported as obsolete but it can't be deleted as it is used by RMAN. The only solution I found was to change the RMAN configuration to use another snapshot controlfile, to remove then the reported obsolete one and to switch back to the default. However, the question remains: why the snapshot controlfile is reported as obsolete?

PS: This happend on a 11gR2 database installed under a Linux x86 platform.

Update: Apparently this is encountered after executing a DUPLICATE database from ACTIVE DATABASE. Furthermore, the snapshot controlfile is reported as a "datafile copy" when a CROSSCHECK is suggested. See below:

RMAN> delete obsolete;                                                                                                                                                                                           

RMAN retention policy will be applied to the command
RMAN retention policy is set to redundancy 1
using channel ORA_DISK_1
using channel ORA_DISK_2
Deleting the following obsolete backups and copies:
Type                 Key    Completion Time    Filename/Handle
-------------------- ------ ------------------ --------------------
Control File Copy     40     30-11-2009 18:41:15 /u01/app/oracle/product/11.2.0/dbhome_1
                                                 /dbs/snapcf_tetris.f

Do you really want to delete the above objects (enter YES or NO)? y                                                                                                                                              

RMAN-06207: WARNING: 1 objects could not be deleted for DISK channel(s) due
RMAN-06208:          to mismatched status.  Use CROSSCHECK command to fix status
RMAN-06210: List of Mismatched objects
RMAN-06211: ==========================
RMAN-06212:   Object Type   Filename/Handle
RMAN-06213: --------------- ---------------------------------------------------
RMAN-06214: Datafile Copy   /u01/app/oracle/product/11.2.0/dbhome_1/dbs/snapcf_tetris.f

Obviously, that can't be a datafile copy. So, let's try a crosscheck as suggested:

RMAN> crosscheck datafilecopy '/u01/app/oracle/product/11.2.0/dbhome_1/dbs/snapcf_tetris.f';                                                                                                                     

using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=148 device type=DISK
allocated channel: ORA_DISK_2
channel ORA_DISK_2: SID=140 device type=DISK
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of crosscheck command at 11/30/2009 19:09:43
RMAN-20230: datafile copy not found in the repository
RMAN-06015: error while looking up datafile copy name: /u01/app/oracle/product/11.2.0
/dbhome_1/dbs/snapcf_tetris.f

Okey, this was expected as I don't have any datafilecopy with that name despite of what RMAN says. So, let's try a crosscheck for the controlfile copy:

RMAN> crosscheck controlfilecopy '/u01/app/oracle/product/11.2.0/dbhome_1/dbs/snapcf_tetris.f';                                                                                                                  

released channel: ORA_DISK_1
released channel: ORA_DISK_2
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=148 device type=DISK
allocated channel: ORA_DISK_2
channel ORA_DISK_2: SID=140 device type=DISK
validation failed for control file copy
control file copy file name=/u01/app/oracle/product/11.2.0/dbhome_1/dbs/snapcf_tetris.f 
RECID=40 STAMP=704313675
Crosschecked 1 objects

As it can be seen the validation fails, although the file exists on that location:

$ ls -al /u01/app/oracle/product/11.2.0/dbhome_1/dbs/snapcf_tetris.f
-rw-r----- 1 oracle oinstall 10436608 Nov 30 18:57 /u01/app/oracle/product/11.2.0/dbhome_1/dbs/snapcf_tetris.f

I don't know if this is documented somewhere but it looks to me like a bug. No idea why the snapshot control file is messed up after a DUPLICATE TARGET DATABASE ... FROM ACTIVE DATABASE.