I just had an interesting discovery, which is almost certainly related to the G600 update... the course needle on my copilot HSI (mechanical) no longer responds to turning the course knob on the HSI. The pointer still moves, but the needle doesn't respond, at least in VOR mode. It is instead slaved to the course needle on the G600... very weird.
Garmin suggested a fix, which involves losing the ability to display the #2 VOR on the G600, and I guess that is the best answer, from a redundancy point of view, but it is annoying to lose capability that I used to have. I used to use the #2 VOR on the bearing pointer on the G600 all the time... now I'll have to use the #1, which again, isn't the end of the world, but it is annoying to have to change.