bucket_engine.c:1909 crash for tap_event=TAP_OPAQUE

Thread 1 (Thread 6028):
#0 0x00007fafde9eea75 in raise () from /lib/libc.so.6
#1 0x00007fafde9f25c0 in abort () from /lib/libc.so.6
#2 0x00007fafde9e7941 in __assert_fail () from /lib/libc.so.6
#3 0x00007fafdd5b1084 in release_handle_locked (h=0x7fafdd7b61a0,
cookie=0x45ddb68) at bucket_engine.c:597
#4 release_handle (h=0x7fafdd7b61a0, cookie=0x45ddb68) at bucket_engine.c:624
#5 get_engine_handle (h=0x7fafdd7b61a0, cookie=0x45ddb68)
at bucket_engine.c:849
#6 0x00007fafdd5b127b in bucket_tap_notify (handle=0x177f, cookie=0x178c,
engine_specific=0x6, nengine=65535, ttl=16 '\020', tap_flags=9169,
tap_event=TAP_OPAQUE, tap_seqno=9525, key=0x11f5b134, nkey=0, flags=0,
exptime=0, cas=0, data=0x11f5b134, ndata=0, vbucket=0)
at bucket_engine.c:1909
#7 0x0000000000409a43 in process_bin_tap_packet (event=TAP_NOOP, c=0x45ddb68)
at daemon/memcached.c:2703
#8 0x000000000040efb5 in process_bin_packet (c=0x45ddb68)
at daemon/memcached.c:2820
#9 complete_nread_binary (c=0x45ddb68) at daemon/memcached.c:3389
#10 0x000000000040f958 in complete_nread (c=0x45ddb68)
at daemon/memcached.c:3471
#11 conn_nread (c=0x45ddb68) at daemon/memcached.c:5275
#12 0x0000000000407263 in event_handler (fd=<value optimized out>,
which=<value optimized out>, arg=0x45ddb68) at daemon/memcached.c:5576
#13 0x00007fafdf5fb3cd in event_process_active_single_queue (base=0x2085a20,
flags=<value optimized out>) at event.c:1308
#14 event_process_active (base=0x2085a20, flags=<value optimized out>)
at event.c:1375
#15 event_base_loop (base=0x2085a20, flags=<value optimized out>)
at event.c:1572
#16 0x0000000000414824 in worker_libevent (arg=0x2084d20)
at daemon/thread.c:304
#17 0x00007fafded439ca in start_thread () from /lib/libpthread.so.0
#18 0x00007fafdeaa16cd in clone () from /lib/libc.so.6
#19 0x0000000000000000 in ?? ()