Assertion failure in arlad

With Arla 0.41, NetBSD 3.99.15:

#0  0xbb9e3d1b in kill () from /usr/lib/libc.so.12
#1  0xbba6d6f7 in abort () from /usr/lib/libc.so.12
#2  0xbba3b0fe in __assert13 () from /usr/lib/libc.so.12
#3  0x0805fe94 in nnpfs_message_create (fd=9, h=0x8128010, size=352)
    at messages.c:836
#4  0x0806b40e in nnpfs_message_receive (fd=9, h=0x8128010, size=352)
    at nnpfs.c:203
#5  0x0805d5ad in process_message (msg_length=352, msg=0x8128010 "`\001", 
    self=0x8128000) at kernel.c:104
#6  0x0805d8db in sub_thread (v_myself=0x8128000) at kernel.c:215
#7  0x0808ca44 in Create_Process_Part2 () at lwp_asm.c:753
#8  0xefeeedec in ?? ()
#9  0x0808e86d in IOMGR_Select (nfds=10, readfds=0xbfbfedd0, writefds=0x0, 
    exceptfds=0x0, timeout=0x0) at iomgr.c:761
#10 0x0805e109 in kernel_interface (args=0xbfbfee24) at kernel.c:493
#11 0x0806c402 in arla_start (device_file=0xbfbfef99 "/dev/nnpfs0", 
    cache_dir=0x80a00f1 "/var/arla") at arlad.c:168
#12 0x0806c56c in main (argc=0, argv=0xbfbfeedc) at arlad.c:278
#13 0x0804a756 in ___start ()

messages.c:836 in my tree is:

    assert_flag(dir_entry,attrusedp);

This happened during a bunch of vos create/mkmount/setacl cycles. After
restarting arlad I continued to do more of same, without problem, so I
don't know how to reproduce this.