Actually, it's not safe to say it worked before. Although on this occasion it was in the German version, it's happened in the English too, not just in XP but in Vista, but seemed to cure itself before we could spot a pattern. This time, the two states appeared in the same playing session, separated only by an Alt-Tab to Windows, then back into the game. Nothing could have been changed during that, because it was a compiled version.
Windows language version in this case is XP SP3 English. Keyboard layout is UK English. Password content not an issue because it doesn't use specifically German characters.
We arrived in the gameplay at the point where the password has to go in. Every entered keystroke got a 'beep' and no text appeared - I don't know where the beep comes from. We called the in-game menu (Exclusive window) and attempted to save - same thing, beeps only, text not accepted. We resumed play, back to the password screen, same thing. So we alt-tabbed to Windows desktop. Then went back into the game. Now, both password field and savegame field would accept text, no beeps anymore.