1script - 7:11 pm on Sep 27, 2011 (gmt 0)
Darn it, Pageone, I envy your memory! I do remember now that as a result of that exchange I've changed the CMS to return better 404s (410s in my case) for all plausible URLs i.e. those that could have been content pages but the particular record cannot be found in the DB, most likely deleted spam. What I forgot to check for was implausible URLs - those that could not be formed into a proper DB lookup and therefore CMS could not handle those. Those URLs received the system default 404 that, it turns out, had a meta refresh to the homepage in the content returned following the 404 header.
You and I had this discussion over a year ago!
Soft 404 reports in WMT disappeared soon after those messages were posted and I moved onto the next issue du jour
Anyway, thanks for the tip! Looks like I've got some work to do now double-checking the 404/410 handling rather than catching those elusive Google raters :)