assert in flusher::step, unable to open database file

I was only able to reproduce this with the php tests, however it did happen every time I ran them.

I did verify that the system worked fine before starting the php tests against it.

memcached log:
sqlite error: unable to open database file
sqlite error: unable to open database file
Exception in flusher loop: unknown database kv_2
memcached: flusher.cc:189: bool Flusher::step(Dispatcher&, TaskId): Assertion `false' failed.


Backtrace:
Thread 1 (process 19143):
#0 0x0000003e5f430265 in raise () from /lib64/libc.so.6
#1 0x0000003e5f431d10 in abort () from /lib64/libc.so.6
#2 0x0000003e5f4296e6 in __assert_fail () from /lib64/libc.so.6
#3 0x00002b4a54262525 in Flusher::step (this=<value optimized out>, d=<value optimized out>, tid=<value optimized out>) at flusher.cc:189
#4 0x00002b4a5426280e in FlusherStepper::callback (this=0x108de9c0, d=@0x10933000, t=<value optimized out>) at flusher.cc:23
#5 0x00002b4a5422a76f in Task::run (this=<value optimized out>, d=@0x10933000, t=<value optimized out>) at dispatcher.hh:133
#6 0x00002b4a542295d3 in Dispatcher::run (this=0x10933000) at dispatcher.cc:116
#7 0x00002b4a5422a003 in launch_dispatcher_thread (arg=0x4ac5) at dispatcher.cc:26
#8 0x0000003e600064a7 in start_thread () from /lib64/libpthread.so.0
#9 0x0000003e5f4d3c2d in clone () from /lib64/libc.so.6