bucket_engine crash during bucket deletion assert(peh->clients == 0);

Thread 4 (Thread 11915):
#0 0x00000037fbacd587 in fdatasync () from /lib64/libc.so.6
#1 0x00002aaaaad7b4a9 in full_fsync (id=<value optimized out>, flags=2)
at embedded/sqlite3.c:25510
#2 unixSync (id=<value optimized out>, flags=2) at embedded/sqlite3.c:25558
#3 0x00002aaaaad98358 in sqlite3WalFrames (pWal=0x1d9948f8, szPage=1024,
pList=0x1d513cf8, nTruncate=18551, isCommit=1, sync_flags=2)
at embedded/sqlite3.c:13413
#4 0x00002aaaaad99128 in sqlite3PagerCommitPhaseOne (pPager=0x1d994498,
zMaster=0x0, noSync=0) at embedded/sqlite3.c:37082
#5 0x00002aaaaad9f627 in sqlite3BtreeCommitPhaseOne (p=0x1d80d7a8,
zMaster=0x0) at embedded/sqlite3.c:47605
#6 0x00002aaaaadd0d4c in vdbeCommit (db=0x1d5e1668, p=<value optimized out>)
at embedded/sqlite3.c:56090
#7 0x00002aaaaadd27bd in sqlite3VdbeHalt (p=0x1ee32d68)
at embedded/sqlite3.c:56514
#8 0x00002aaaaae2133a in sqlite3VdbeExec (p=0x1ee32d68)
at embedded/sqlite3.c:60326
#9 0x00002aaaaae00d5a in sqlite3Step (pStmt=0x1ee32d68)
at embedded/sqlite3.c:57947
#10 sqlite3_step (pStmt=0x1ee32d68) at embedded/sqlite3.c:58011
#11 0x00002aaaaad6f999 in PreparedStatement::execute (this=0x45b18690)
at sqlite-pst.cc:73
#12 0x00002aaaaad70e48 in SqliteStrategy::execute (
this=<value optimized out>, query=<value optimized out>)
at sqlite-strategies.cc:151
#13 0x00002aaaaad712b4 in ShardedByVBucketSqliteStrategy::destroyTables (
this=0x1b212c00) at sqlite-strategies.cc:417
#14 0x00002aaaaad6da4f in StrategicSqlite3::reset (this=0x1b212ce0)
at sqlite-kvstore.cc:145
#15 0x00002aaaaad00fce in EventuallyPersistentStore::flushOneDeleteAll (
this=0x1b4e0730) at ep.cc:1733
#16 0x00002aaaaad0ac9d in EventuallyPersistentStore::flushOne (
this=0x1b4e0730, q=0x1b4e0860, rejectQueue=0x1d98f6f0) at ep.cc:1872
#17 0x00002aaaaad0ae8e in EventuallyPersistentStore::flushSome (
this=0x1b4e0730, q=0x1b4e0860, rejectQueue=0x1d98f6f0) at ep.cc:1489
#18 0x00002aaaaad40eea in Flusher::doFlush (this=0x1d1df2c0) at flusher.cc:242
#19 0x00002aaaaad4194a in Flusher::step (this=0x67, d=...,
tid=Traceback (most recent call last):
File "/usr/share/gdb/python/libstdcxx/v6/printers.py", line 32, in to_string
return '%s (count %d) %s' % (self.typename,
TypeError: int argument required
) at flusher.cc:156
#20 0x00002aaaaad421be in FlusherStepper::callback (this=0x1c41fe40, d=...,
t=<value optimized out>) at flusher.cc:23
#21 0x00002aaaaacff2df in Task::run (this=<value optimized out>, d=...,
t=<value optimized out>) at dispatcher.hh:139
#22 0x00002aaaaacfdeaf in Dispatcher::run (this=0x1c2a20f0)
at dispatcher.cc:119
#23 0x00002aaaaacfe8e3 in launch_dispatcher_thread (arg=0x67)
at dispatcher.cc:28
#24 0x00000037fc60673d in start_thread () from /lib64/libpthread.so.0
#25 0x00000037fbad3f6d in clone () from /lib64/libc.so.6

Thread 3 (Thread 11916):
#0 0x00000037fc60b150 in pthread_cond_timedwait@@GLIBC_2.3.2 ()
from /lib64/libpthread.so.0
#1 0x00002aaaaacfbb60 in wait (this=0x1d1df200, d=...) at syncobject.hh:42
#2 IdleTask::run (this=0x1d1df200, d=...) at dispatcher.cc:244
#3 0x00002aaaaacfdeaf in Dispatcher::run (this=0x1d1ddff0)
at dispatcher.cc:119
#4 0x00002aaaaacfe8e3 in launch_dispatcher_thread (arg=0x1d1de044)
at dispatcher.cc:28
#5 0x00000037fc60673d in start_thread () from /lib64/libpthread.so.0
#6 0x00000037fbad3f6d in clone () from /lib64/libc.so.6

Thread 2 (Thread 11917):
#0 0x00000037fc60b150 in pthread_cond_timedwait@@GLIBC_2.3.2 ()
from /lib64/libpthread.so.0
#1 0x00002aaaaad1ce07 in wait (this=0x1b209e10) at syncobject.hh:42
#2 wait (this=0x1b209e10) at tapconnmap.hh:185
#3 EventuallyPersistentEngine::notifyTapIoThread (this=0x1b209e10)
at ep_engine.cc:3695
#4 0x00002aaaaad1cf71 in EvpNotifyTapIo (arg=0x1b209e10) at ep_engine.cc:894
#5 0x00000037fc60673d in start_thread () from /lib64/libpthread.so.0
#6 0x00000037fbad3f6d in clone () from /lib64/libc.so.6

Thread 1 (Thread 11959):
#0 0x00000037fba30265 in raise () from /lib64/libc.so.6
#1 0x00000037fba31d10 in abort () from /lib64/libc.so.6
#2 0x00000037fba296e6 in __assert_fail () from /lib64/libc.so.6
#3 0x00002aaaaaaaebc1 in engine_shutdown_thread (arg=0x1b1d5bd0)
at bucket_engine.c:1401
#4 0x00000037fc60673d in start_thread () from /lib64/libpthread.so.0
#5 0x00000037fbad3f6d in clone () from /lib64/libc.so.6