panic: "pb->pb_pathcopyuses == 0" failed (sys_rename)

[Frank Kardel <kardel%netbsd.org@localhost>]

When booting a 20121225 kernel running a 6.99.5 userland
I get

panic: kernel diagnostic assertion "pb->pb_pathcopyuses == 0" failed: 
file "/usr/src/sys/kern/vfs_lookup.c", line 279
cpu0: Begin traceback...
kern_assert() at netbsd:kern_assert+0x48
pathbuf_destroy() at netbsd:pathbuf_destroy+0x6c
do_sys_renameat() at netbsd:do_sys_renameat+0x82
sys_rename() at netbsd:sys_rename+0x25
syscall() at netbsd:syscall+0x94
--- syscall (number 128) ---
7f7ff36396da:
cpu0: End traceback...

when logging in kde.

Any clues?

Frank