I wouldn't have though this was a problem of logic. If you have all the right diodes in all the right places (which you probably have by default) then you can't get current running backwards. You're also unlikely to get 10A out of 125W panel more like 8 as max so the CB at 10A should be okay. I think maybe Occam's razor is called for - the most likely cause is the right one - a bit of equipment failure. Why have you got a CB in the line at all? Just in case something shorts somewhere?
David Berry, "Time to go South" Kindle books