When I complained about the severe stuttering I was getting with my iFly 737 (in another post) I was also getting stuttering in all my other planes when turning on/off lights.
Last week I noticed that I was not getting any stuttering in the leveld 767 so for a test I loaded up the iFly ( stuttering had been so bad I had stopped using it) and the stuttering had also disappeared.
I have no idea what I did or didn't do that stopped the stuttering.
I did recently purchase and install new Orbx scenery and just flights free 757, maybe that did something.