freebsd 5.1 ohci driver causing a panic

I can reproduce a kernel panic in 5.1 by unplugging the usb cable from my
UPS. Unfortunately I'm not getting crash dumps. I'm not sure if I'm doing
something wrong.  I have dumpdev set in /etc/rc.conf, but I also notice
that the panic screen says ad0 DRQ timeout so I'm not sure if that is the
reason I don't get a dump.

Anyway, I saw in CVS logs that the ohci driver has been updated a lot
since 5.1 and I was wondering if anyone knows if any of the changes fix
this type of panic.  I couldn't tell from the logs, but I'm currently
cvsup'ing to 5.2 so I get the more recent ohci driver.

Let me know if there is anything else I should do.

Michael