Given the many problems with online requirements while playing with Steam offline, it was most due.
Lots of core files got updated, new gamemanager.dll, serz.exe, tunnel shaders and some more files.
Playing offline seems to work, but the Steam overlay is still live which makes no sense to me as the main Steam application window stays black and void.
The Steam application window shows an empty cached file ///D:/steam/steam/cached/offline-english.html, but when clicking the menu entries above, the "loading" gizmo spins yet nothing happens.
What browser is working in that overlay, is it safe and secure?
Makes me wonder how "offline" I am when I am off line?

Hopefully some other issues have been resolved. Will RSC provide some info quick?