Andy_Langton - 11:42 pm on Oct 26, 2012 (gmt 0)

Parameter handling via GWT is a "suggestion" to Google as to how to handle parameters. IMO, this is weaker even than the rel canonical attribute, which is itself not reliable.

if you think these parameters are causing a real issue with performance, then force a redirect from them to the rewritten version so they get dropped from Google's map (almost) entirely.

Of course, Google is URL-hungry, so it may be that these represent an insignificant problem that does not need to be fixed. That said, if you're the tidy type, I'd suggest you fix them without using Google's proprietary method - which may not fix them at all :)