[Users] Claws crashes because it's already running?

[Graham P Davis]

Claws sometimes just freezes for a few minutes and then disappears from
the screen. The error message that I get when running from the console
is a little confusing:

claws.c:102:Starting Claws Mail version Claws Mail 3.13.2
utils.c:1802:using default rc_dir /home/graham/.claws-mail
main.c:2177:Using control socket /tmp/claws-mail-2000/ca5d42c47df9fea238d06858b40ea873
main.c:2272:another Claws Mail instance is already running.

No message as to why it stopped but says it can't start because it
hasn't stopped? what's that all about? why is it trying to start if it
hasn't stopped?

-- 
Graham P Davis, Bracknell, Berks.
OS: Linux: openSUSE 13.2 (64-bit); KDE 4.14.9; Kernel: 4.4.1