Strange DataGuard behaviour

I have been tested a new features of 11g Data Guard. During that I have change a database protection mode into Maximum Protection
and after that make some test with startup and shutdown of both databases.
As expected when primary database was online I have got following error on console and warning in alert.log

SQL> shutdown immediate
ORA-01154: database busy. Open, close, mount, and dismount not allowed now

Alert.log
Attempt to shut down Standby Database
Standby Database operating in NO DATA LOSS mode
Detected primary database alive, shutdown primary first, shutdown aborted

That’s expected results. But in next test case when I shutdown a primary database I still got that same error !

SQL> shutdown immediate
ORA-01154: database busy. Open, close, mount, and dismount not allowed now

I have rerun disabling command for recovery process and checked if recovery mode is disabled

SQL>ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;
Database altered.
SQL> SELECT RECOVERY_MODE FROM V$ARCHIVE_DEST_STATUS;

RECOVERY_MODE
-----------------------
IDLE
IDLE
IDLE
IDLE
IDLE
IDLE
IDLE
IDLE
IDLE
IDLE
IDLE

11 rows selected.

Hmmm .... of course I can shutdown that database using abort but I don’t want to.
Let’s check what else can prevent database to shutdown – a little check what processes are running and EUREKA – dataguard broker is still running. So:

SQL> alter system set dg_broker_start=FALSE scope=memory;
System altered.

SQL> shutdown immediate
ORA-01109: database not open
Database dismounted.
ORACLE instance shut down.
SQL>

Uffff .....
Other question is why ? If primary database was down, standby database should be stopped without any other circumstances.

regards,
Marcin