xl hangs on list/destroy

[David Krinsky <krinsky%bantha.org@localhost>]

I have a small server on which I'm running a NetBSD 6.1.4 dom0 and
xentools42/xenkernel42 from pkgsrc.  The dom0 does essentially nothing
except serve as the dom0; there are two PV domUs - one NetBSD, one
Linux.  

For the most part this setup works well, but when I need to reboot one
of the domUs, xl will often hang on either xl destroy or xl shutdown
(I've tried shutting down the domUs both ways).  Once it does, all
further xl commands, including xl list, hang--as though there's a
deadlock somewhere--and the only fix I've been able to come up with is
to reboot the dom0 (after which everything starts up fine).

/var/log/xen/xl-abcd.log has a single line along these lines:

Waiting for domain abcd (domid 1) to die [pid 518]

Otherwise, there are no errors/messages in obvious log files, on the
console, or on the command line.

Does this sound like a familiar bug (or familiar newbie error) to
anyone?  Any ideas how to go about debugging it?

Thanks in advance for any suggestions.

D.