I was sitting around experimenting with my system last night and listening to music. I usually have my front mains set to small but on a whim set the front's to Large and no sub. In listening to Stereo-Upsample I realized that as I changed the crossover the higher I went (say from 60 to 80) the more bass I got. I thought it would be the opposite, the higher the crossover the less bass I would get.

It is a bit embarrassing after all these years but am I complete idiot and been thinking wrong?

That sounds correct. You are allowing the sub to work on a wider spectrum (20Hz-80Hz, rather than a narrower 20Hz-60Hz). I guess it all depends on the frequency your fronts roll-off when setting up the sub.

I ran into the same bug a few months ago. You are not totally stupid. I logged an issue with the Outlaws for this same issue back when I ran into it.. Have you applied the latest firmware update? I believe that is one of the bugs that is fixed in the latest firmware. When the front’s are set to large, the X-over should not change the output to the front's at all no matter what.

This may or may not be related. I've noticed that when I change from a 7.1 processing mode to Stereo upsample I still see the icon for all 7 speakers displayed on the front pannel.
Could this additional bass in the mains be contributed by the "small" speakers' crossovers ?
( I haven't installed the update )