DBPITR and ORA-16005 Error: database requires recovery.

Hi,

 I am trying to test database point in time recovery scenarios in
which I want to Open read-only the database before using RESETLOGS
clause. The test was ran on a Oracle 10gR2 single instance.

1) Perform backup using RMAN default channel, no recovery catalog and
having control file autobackup enabled.
RUN {
BACKUP DATABASE;
BACKUP ARCHIVELOG ALL NOT BACKED UP DELETE ALL INPUT;
}

2) Get the current SCN from V$DATABASE. Call it SCN1.

3) DROP a table. Shutdown Immediate and mount the database.

4) Perform a DBPITR up to SCN1:
RUN {
SET UNTIL SCN [SCN1];
RESTORE DATABASE;
RECOVER DATABASE;
}

5) When trying to open the database in read only mode
RMAN> SQL 'ALTER  DATABASE OPEN READ ONLY'
 The command fails with ORA-16005: database requires recovery.

I can only open the database read-write using RESETLOGS clause, but
this leave me without the chance of verifying the data before creating
a new database incarnation.

Does anyone have any clue about why is this happening?

Thanks for your help.

G. Bahut.