Nut upsuser - Mar 2012 - ups.delay.shutdown ignored on apc_smartups_3000_xl

Hello,
I run nut 2.4.3 under Debian Squeeze 6.0, using an APC Smart UPS 3000 XL
connected via USB.
The communication between Nut and the Ups is working, and when Nut feels
the low battery signal, it starts shudown.
Unfortunately the shutdown procedure is very long, more than 7 minutes,
so I need to wait at least 10 minutes to be safe, before the power is
really cut.

I tried to setup these values in /etc/rc.local:

 /bin/upsrw -u local_mon -p mypass -s ups.delay.shutdown=600
apc_smartups_3000_xl
/bin/upsrw -u local_mon -p mypass -s battery.charge.low=40
apc_smartups_3000_xl
/bin/upsrw -u local_mon -p mypass -s battery.runtime.low=900
apc_smartups_3000_xl

And also configured the driver in /etc/nut/ups.conf as is:

[apc_smartups_3000_xl]
    driver = usbhid-ups
    port = auto
    offdelay=600
    ondelay=-1

But everytime the UPS cuts the power after less than 5 minutes. The
battery is charged enough when the ups cuts the power.

Suggestions ?

Thank you,
--
Gabriele