So you (sorry, obvious dumb question here) have the same SX100 control panel that's legacy from the SX50? And I'm guessing this problem didn't occur until after you updated to 6.2?
That seems like something that would be firmware controlled, and I'm really hoping the software isn't updating the firmware randomly, but I also assume that 6.2 comes with updated firmware and maybe that has a bug in it?
Other than that, you got me. Sounds like the type of mystery problem I usually have, so you have my sympathies.