Str82u - 4:09 pm on Mar 27, 2013 (gmt 0)
We had a similar problem but it was because of a ?url.string to deactivate mobile. It sounds like you've got your bases covered though if you've added rel-canonical. Our solution was "URL Parameters" in GWT but I wouldn't use a redirect to move desktops and mobile devices around to the proper sites.
I'm not certain if you'd get dinged for redirecting just Gbot from your mobile subdomain to main domain but it's what I'd look into.