I thought you might be left-handed from that as I tend to find reading upside-down natural and am 'sinister'. But then, that could be from years of reading children's books upside-down to the rugrats.

There does seem to be a link with backwards rather than forwards, which made me think of it - when someone in a pub asked me the time once I looked at the clock on the wall and responded correctly instantly, not noticing it was a gimmick one and was actually back-to-front.