1script - 5:27 pm on Sep 27, 2011 (gmt 0)
Thanks, Pageone! Well, what do you know: this 404.shtml was on the server for at least the last four years. The critical mass of junk redirecting to the homepage got to the banning point? Fixed that, looks like another recon request is in order...
I do believe Google interprets that directive as a 301.
This looks like a technicality Google WMT could/would notify the webmaster about, no? I remember a wave of Soft-404 errors in WMT that came and went almost as quickly about a year ago. It looks like the same thing to me... Anyhow, we'll see how this pans out in another month or so.