zfs panic, solaris_assert

[Attila Nagy]

Hi,

Since running svn revision r243704 I get frequent panics:
panic: solaris assert: sa.sa_magic == 0x2F505A (0x4f22a8ed == 0x2f505a),
file: 
/data/usr/src/sys/modules/zfs/../../cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vfsops.c, 
line: 597
cpuid = 0
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2a
kdb_backtrace() at kdb_backtrace+0x37
panic() at panic+0x1ce
assfail3() at assfail3+0x29
zfs_space_delta_cb() at zfs_space_delta_cb+0xbe
dmu_objset_userquota_get_ids() at dmu_objset_userquota_get_ids+0x142
dnode_sync() at dnode_sync+0xc5
dmu_objset_sync_dnodes() at dmu_objset_sync_dnodes+0x5d
dmu_objset_sync() at dmu_objset_sync+0x17f
dsl_pool_sync() at dsl_pool_sync+0xca
spa_sync() at spa_sync+0x34a
txg_sync_thread() at txg_sync_thread+0x139
fork_exit() at fork_exit+0x11f
fork_trampoline() at fork_trampoline+0xe
--- trap 0, rip = 0, rsp = 0xffffff90231accf0, rbp = 0 ---

I can't tell whether it's the data or the code. If the latter, is this 
fixed in later revisions?
If it's the file system, what can I do with this?