[STUMP] Can somebody decrypt stumpwm's backtrace to me, please.

[stumpwm]

Hello, stumpwm-devel list.

I'm not experienced in CLISP, but appreciate StumpWM so I am it's user.

But it sometimes produce some backtraces and then restarts (and loses all
windows configuration), so this annoys a lot.
It usually happens when I switch windows. But sometimes when new window appear.

Backtrace of attempt of switching between two groups is in attachment,
can you please decrypt that and tell me what can be the reason of exceptions,
if that is visible. Can this be related to windows titles (their encodings)?

And what can I do to get/provide some more information?
Thanks a lot.

stumpwm.backtrace.log
Description: Text document