> Then try start/control panel/folder options/view tab and see if hide
> extensions for known file types is checked or unchecked.
It was a problem with the known file types setting, though a slightly strange one. I forgot to say that I don't run NTB directly from my limited user account; I use a runas to run it from my administrator account (so I can use it to change any file). The suddenly changed known file types setting was not displayed either in my user account or my admin account, but only when viewing the folder view settings from a runas in the exact same way.
Thanks a lot!