P-OUT clear service action hanging

I'm running passthrough commands to a LUN on an MSA1000. My host is running RH9. I'm using the sg driver provided with this distribution using the SG_IO option to send the passthrough commands.

I have a previously established reservation that I'm trying to clear. I'm following the directions in the spec for clearing a a persistent reservation - specifically, section 5.5.3.6.5 of SPC-2:

(1) My P-OUT command has a service action set to CLEAR 03h.
(2) In my 24 bytes of data transferred to the target with the command, only the reservation key field is set to a non-zero value. This value is of course the
previously registered reservation key.

When I execute this command, my driver hangs until it times out and returns with an error.

Any ideas or history with the MSA1000 that makes it not cooperate well with P-IN/P-OUT commands?

Thanks,
Brian