Do you have a specific set of repro steps for this? I just changed my timezone multiple times while Steam was running and had no problems.
Changing timezone should not generate a usable test case, it may be possible to reproduce by using the date command to shift the system time. The steam client has been sensitive to unexpected time shifts either by ntp or by a daylight savings shift. It can also react poorly to leap seconds. I've only seen one of the threads max out a core when it shouldn't and the client was still usable. (There's a forum posting by me reporting this before this issue tracker was setup.)
EDIT: Old reference - http://steamcommunity.com/app/221410/discussions/0/882965239825362811/
It seems updated and I can't catch this bug again... Anyway, thanks. :)
Nothing extracted yet.
I corrected my system time(just time zone problems) and... Steam not works until I restart (only SIGKILL :( ) him.
My system: http://pastebin.com/Jdaej75z (sorry, it on Russian).