I've got a friend who has spent 250 hours (within 2 months) playing this game on Steam and he claims that this problem occured after the latest patch has been installed (20th-september).
Some examples include the situation that he becomes logged out when I want to join his friend in other city centre.
and what about double-displayed stats (helmets and armour)?
Steam had an upset earlier in the week, shortly after the SK patch came out. Its not known if its directly related or not since only a small segment of Steam users (in general) were having issues with the steam client.