abort in EventuallyPersistentStore::completeBGFetch during regression tests

During the regression tests, I believe while running rebalancetests.IncrementalRebalanceInTests.test_load,keys-count=100000,replica=2,delete-ratio=0,expiry-ratio=0

Program terminated with signal 6, Aborted.
#0 0x00002accaa061265 in raise () from /lib64/libc.so.6

Thread 13 (Thread 0x2accaa899240 (LWP 32241)):
#0 0x00002accaa1058a8 in epoll_wait () from /lib64/libc.so.6
#1 0x00002acca9312ba6 in epoll_dispatch (base=0x11bb0000, tv=<value optimized out>) at epoll.c:404
#2 0x00002acca9301c11 in event_base_loop (base=0x11bb0000, flags=0) at event.c:1558
#3 0x00000000004095b2 in main (argc=<value optimized out>, argv=<value optimized out>) at daemon/memcached.c:7901

Thread 12 (Thread 32247):
#0 0x00002accaa0f778b in read () from /lib64/libc.so.6
#1 0x00002accaa09dd57 in _IO_new_file_underflow () from /lib64/libc.so.6
#2 0x00002accaa09e71e in _IO_default_uflow_internal () from /lib64/libc.so.6
#3 0x00002accaa099fdb in getc () from /lib64/libc.so.6
#4 0x00002accaa89a879 in check_stdin_thread (arg=0x4033f0) at extensions/daemon/stdin_check.c:19
#5 0x00002acca9e1c73d in start_thread () from /lib64/libpthread.so.0
#6 0x00002accaa1054bd in clone () from /lib64/libc.so.6

Thread 11 (Thread 32251):
#0 0x00002accaa0cb541 in nanosleep () from /lib64/libc.so.6
#1 0x00002accaa0cb364 in sleep () from /lib64/libc.so.6
#2 0x0000000000415ca8 in check_isasl_db_thread (arg=<value optimized out>) at daemon/isasl.c:233
#3 0x00002acca9e1c73d in start_thread () from /lib64/libpthread.so.0
#4 0x00002accaa1054bd in clone () from /lib64/libc.so.6

Thread 10 (Thread 32252):
#0 0x00002accaa1058a8 in epoll_wait () from /lib64/libc.so.6
#1 0x00002acca9312ba6 in epoll_dispatch (base=0x11bb0500, tv=<value optimized out>) at epoll.c:404
#2 0x00002acca9301c11 in event_base_loop (base=0x11bb0500, flags=0) at event.c:1558
#3 0x0000000000414074 in worker_libevent (arg=0xd750500) at daemon/thread.c:305
#4 0x00002acca9e1c73d in start_thread () from /lib64/libpthread.so.0
#5 0x00002accaa1054bd in clone () from /lib64/libc.so.6

Thread 9 (Thread 32253):
#0 0x00002accaa1058a8 in epoll_wait () from /lib64/libc.so.6
#1 0x00002acca9312ba6 in epoll_dispatch (base=0x11bb0280, tv=<value optimized out>) at epoll.c:404
#2 0x00002acca9301c11 in event_base_loop (base=0x11bb0280, flags=0) at event.c:1558
#3 0x0000000000414074 in worker_libevent (arg=0xd750600) at daemon/thread.c:305
#4 0x00002acca9e1c73d in start_thread () from /lib64/libpthread.so.0
#5 0x00002accaa1054bd in clone () from /lib64/libc.so.6

Thread 8 (Thread 32254):
#0 0x00002accaa1058a8 in epoll_wait () from /lib64/libc.so.6
#1 0x00002acca9312ba6 in epoll_dispatch (base=0x11bb0c80, tv=<value optimized out>) at epoll.c:404
#2 0x00002acca9301c11 in event_base_loop (base=0x11bb0c80, flags=0) at event.c:1558
#3 0x0000000000414074 in worker_libevent (arg=0xd750700) at daemon/thread.c:305
#4 0x00002acca9e1c73d in start_thread () from /lib64/libpthread.so.0
#5 0x00002accaa1054bd in clone () from /lib64/libc.so.6

Thread 7 (Thread 32255):
#0 0x00002accaa1058a8 in epoll_wait () from /lib64/libc.so.6
#1 0x00002acca9312ba6 in epoll_dispatch (base=0x11bb0a00, tv=<value optimized out>) at epoll.c:404
#2 0x00002acca9301c11 in event_base_loop (base=0x11bb0a00, flags=0) at event.c:1558
#3 0x0000000000414074 in worker_libevent (arg=0xd750800) at daemon/thread.c:305
#4 0x00002acca9e1c73d in start_thread () from /lib64/libpthread.so.0
#5 0x00002accaa1054bd in clone () from /lib64/libc.so.6

Thread 6 (Thread 32256):
#0 0x00002accaa1058a8 in epoll_wait () from /lib64/libc.so.6
#1 0x00002acca9312ba6 in epoll_dispatch (base=0x11bb0780, tv=<value optimized out>) at epoll.c:404
#2 0x00002acca9301c11 in event_base_loop (base=0x11bb0780, flags=0) at event.c:1558
#3 0x0000000000414074 in worker_libevent (arg=0xd750900) at daemon/thread.c:305
#4 0x00002acca9e1c73d in start_thread () from /lib64/libpthread.so.0
#5 0x00002accaa1054bd in clone () from /lib64/libc.so.6

Thread 5 (Thread 32257):
#0 0x00002accaa0cb541 in nanosleep () from /lib64/libc.so.6
#1 0x00002accaa0feed4 in usleep () from /lib64/libc.so.6
#2 0x00002aaaaad6c0c2 in updateStatsThread (arg=0xd74e7c0) at memory_tracker.cc:31
#3 0x00002acca9e1c73d in start_thread () from /lib64/libpthread.so.0
#4 0x00002accaa1054bd in clone () from /lib64/libc.so.6

Thread 4 (Thread 32259):
#0 0x00002acca9e21150 in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
#1 0x00002aaaaad2ada0 in wait (this=0x11c18000, d=...) at syncobject.hh:47
#2 IdleTask::run (this=0x11c18000, d=...) at dispatcher.cc:294
#3 0x00002aaaaad2d390 in Dispatcher::run (this=0x11bfac40) at dispatcher.cc:123
#4 0x00002aaaaad2dc1b in launch_dispatcher_thread (arg=<value optimized out>) at dispatcher.cc:28
#5 0x00002acca9e1c73d in start_thread () from /lib64/libpthread.so.0
#6 0x00002accaa1054bd in clone () from /lib64/libc.so.6

Thread 3 (Thread 32260):
#0 0x00002acca9e21150 in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
#1 0x00002aaaaad2ada0 in wait (this=0x11c18080, d=...) at syncobject.hh:47
#2 IdleTask::run (this=0x11c18080, d=...) at dispatcher.cc:294
#3 0x00002aaaaad2d390 in Dispatcher::run (this=0x11bfb880) at dispatcher.cc:123
#4 0x00002aaaaad2dc1b in launch_dispatcher_thread (arg=<value optimized out>) at dispatcher.cc:28
#5 0x00002acca9e1c73d in start_thread () from /lib64/libpthread.so.0
#6 0x00002accaa1054bd in clone () from /lib64/libc.so.6

Thread 2 (Thread 32261):
#0 0x00002acca9e21150 in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
#1 0x00002aaaaad4b15f in wait (this=0x11c06000) at syncobject.hh:47
#2 wait (this=0x11c06000) at syncobject.hh:63
#3 wait (this=0x11c06000) at tapconnmap.hh:171
#4 EventuallyPersistentEngine::notifyPendingConnections (this=0x11c06000) at ep_engine.cc:3390
#5 0x00002aaaaad4b243 in EvpNotifyPendingConns (arg=0x11c06000) at ep_engine.cc:1106
#6 0x00002acca9e1c73d in start_thread () from /lib64/libpthread.so.0
#7 0x00002accaa1054bd in clone () from /lib64/libc.so.6

Thread 1 (Thread 0x46c37940 (LWP 32258)):
#0 0x00002accaa061265 in raise () from /lib64/libc.so.6
#1 0x00002accaa062d10 in abort () from /lib64/libc.so.6
#2 0x00002accaa05a6e6 in __assert_fail () from /lib64/libc.so.6
#3 0x00002aaaaad3cd7e in EventuallyPersistentStore::completeBGFetch (this=0x11c38000, key="44815-ca79406", vbucket=<value optimized out>, vbver=<value optimized out>, rowid=1, cookie=0x11b31340, init=684660370523677,
type=BG_FETCH_VALUE) at ep.cc:1250
#4 0x00002aaaaad49305 in BGFetchCallback::callback(Dispatcher&, std::tr1::shared_ptr<Task>) () from /opt/couchbase/lib/memcached/ep.so
#5 0x00002aaaaad2e4df in Task::run(Dispatcher&, std::tr1::shared_ptr<Task>) () from /opt/couchbase/lib/memcached/ep.so
#6 0x00002aaaaad2d390 in Dispatcher::run (this=0x11bfaa80) at dispatcher.cc:123
#7 0x00002aaaaad2dc1b in launch_dispatcher_thread (arg=<value optimized out>) at dispatcher.cc:28
#8 0x00002acca9e1c73d in start_thread () from /lib64/libpthread.so.0
#9 0x00002accaa1054bd in clone () from /lib64/libc.so.6