ZFS panic (dn->dn_datablkshift != 0) with r256304 and send/recv

I get the following assert failure with a recent current:

panic: solaris assert: dn->dn_datablkshift != 0, file: /usr/src/sys/modules/zfs/../../cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_tx.c, line: 638

# uname -a
FreeBSD freebsd10 11.0-CURRENT FreeBSD 11.0-CURRENT #0 r256304: Thu Oct 10 19:38:55 EDT 2013     kwhite_at_freebsd10:/tank/obj/usr/src/sys/GENERIC  amd64

# kgdb /boot/kernel/kernel /var/crash/vmcore.last
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Unread portion of the kernel message buffer:
...
<118># zfs send -vi tank/RPI_at_20131004 tank/RPI_at_20131013 | zfs recv -vF m_tank/RPI_at_20131013
<118>send from _at_20131004 to tank/RPI_at_20131013 estimated size is 85.0M
<118>total estimated size is 85.0M
<118>TIME        SENT   SNAPSHOT
<118>receiving incremental stream of tank/RPI_at_20131013 into m_tank/RPI_at_20131013
<118>19:45:12   5.90M   tank/RPI_at_20131013
<118>19:45:13   36.4M   tank/RPI_at_20131013
<118>19:45:15   38.4M   tank/RPI_at_20131013
<118>19:45:16   41.3M   tank/RPI_at_20131013
panic: solaris assert: dn->dn_datablkshift != 0, file: /usr/src/sys/modules/zfs/../../cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_tx.c, line: 638
cpuid = 0
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe00977711a0
kdb_backtrace() at kdb_backtrace+0x39/frame 0xfffffe0097771250
vpanic() at vpanic+0x126/frame 0xfffffe0097771290
panic() at panic+0x43/frame 0xfffffe00977712f0
assfail() at assfail+0x22/frame 0xfffffe0097771300
dmu_tx_hold_free() at dmu_tx_hold_free+0x162/frame 0xfffffe00977713e0
dmu_free_long_range() at dmu_free_long_range+0x244/frame 0xfffffe0097771450
dmu_free_long_object() at dmu_free_long_object+0x1f/frame 0xfffffe0097771480
dmu_recv_stream() at dmu_recv_stream+0x86e/frame 0xfffffe00977716b0
zfs_ioc_recv() at zfs_ioc_recv+0x96c/frame 0xfffffe0097771920
zfsdev_ioctl() at zfsdev_ioctl+0x54a/frame 0xfffffe00977719c0
devfs_ioctl_f() at devfs_ioctl_f+0xf0/frame 0xfffffe0097771a20
kern_ioctl() at kern_ioctl+0x2ca/frame 0xfffffe0097771a90
sys_ioctl() at sys_ioctl+0x11f/frame 0xfffffe0097771ae0
amd64_syscall() at amd64_syscall+0x265/frame 0xfffffe0097771bf0
Xfast_syscall() at Xfast_syscall+0xfb/frame 0xfffffe0097771bf0
--- syscall (54, FreeBSD ELF64, sys_ioctl), rip = 0x8019f49ca, rsp = 0x7fffffff9438, rbp = 0x7fffffff94c0 ---
KDB: enter: panic
Uptime: 7m30s
...
(kgdb) where
#0  doadump (textdump=1) at pcpu.h:219
#1  0xffffffff808b88b7 in kern_reboot (howto=260) at /usr/src/sys/kern/kern_shutdown.c:447
#2  0xffffffff808b8dc5 in vpanic (fmt=<value optimized out>, ap=<value optimized out>) at /usr/src/sys/kern/kern_shutdown.c:754
#3  0xffffffff808b8e13 in panic (fmt=<value optimized out>) at /usr/src/sys/kern/kern_shutdown.c:683
#4  0xffffffff81dd1222 in assfail (a=<value optimized out>, f=<value optimized out>, l=<value optimized out>) at /usr/src/sys/modules/opensolaris/../../cddl/compat/opensolaris/kern/opensolaris_cmn_err.c:81
#5  0xffffffff81c847c2 in dmu_tx_hold_free (tx=0xfffff800118bda00, object=<value optimized out>, off=<value optimized out>, len=<value optimized out>)
     at /usr/src/sys/modules/zfs/../../cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_tx.c:638
#6  0xffffffff81c78124 in dmu_free_long_range (os=0xfffff8000580f000, object=<value optimized out>, offset=0, length=18446744073709551615)
     at /usr/src/sys/modules/zfs/../../cddl/contrib/opensolaris/uts/common/fs/zfs/dmu.c:654
#7  0xffffffff81c781df in dmu_free_long_object (os=0xfffff8000580f000, object=66055) at /usr/src/sys/modules/zfs/../../cddl/contrib/opensolaris/uts/common/fs/zfs/dmu.c:700
#8  0xffffffff81c7c39e in dmu_recv_stream (drc=0xfffffe0097771728, fp=<value optimized out>, voffp=0xfffffe0097771718, cleanup_fd=8, action_handlep=<value optimized out>)
     at /usr/src/sys/modules/zfs/../../cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_send.c:1289
#9  0xffffffff81d0a1fc in zfs_ioc_recv (zc=0xfffffe0001830000) at /usr/src/sys/modules/zfs/../../cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_ioctl.c:4102
#10 0xffffffff81d054ea in zfsdev_ioctl (dev=<value optimized out>, zcmd=<value optimized out>, arg=<value optimized out>, flag=<value optimized out>, td=<value optimized out>)
     at /usr/src/sys/modules/zfs/../../cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_ioctl.c:5960
#11 0xffffffff807b0d40 in devfs_ioctl_f (fp=0xfffff80005304dc0, com=3222821403, data=0xfffff800027abc40, cred=<value optimized out>, td=0xfffff8000524f000) at /usr/src/sys/fs/devfs/devfs_vnops.c:757
#12 0xffffffff8090ffea in kern_ioctl (td=0xfffff8000524f000, fd=<value optimized out>, com=0) at file.h:319
#13 0xffffffff8090fccf in sys_ioctl (td=0xfffff8000524f000, uap=0xfffffe0097771b80) at /usr/src/sys/kern/sys_generic.c:698
#14 0xffffffff80cb2e05 in amd64_syscall (td=0xfffff8000524f000, traced=0) at subr_syscall.c:134
#15 0xffffffff80c979fb in Xfast_syscall () at /usr/src/sys/amd64/amd64/exception.S:391
#16 0x00000008019f49ca in ?? ()
Previous frame inner to this frame (corrupt stack?)
Current language:  auto; currently minimal
(kgdb)

...keith