stalling

With star 1.5.2 on the latest Solaris 10, we are seeing star appear to
stall in the middle of dumping a ZFS snapshot to tape. Attaching dtruss,
iosnoop, and opensnoop to the affected process shows no activity. We
invoke star with:

  star -C /path/to/.zfs/snapshot/20130407 -c -S -acl artype=exustar \
	-sparse -time -xdev \
	-multivol -wtardumps -new-volume-script=/usr/local/sbin/mtx-next \
	errctl=/usr/local/etc/star-errctl.conf \
	-not pat=*/.Trash/* pat=*/.cache/* pat=*/.thumbnails/* pat=*/.nfs* \
	level=0 fs-name=/path/to blocks=512 file=/dev/rmt/1cn .

I don't believe it is a problem with the tape device since we can kill the
hanging star and run another (on another filesystem) right after which
runs to completion.

Does anything above suggest why the star process stalls or waits?

How can one debug this further?

Thanks for your time,
Ryan