Autopilot induced oscillation

Don't know if you guys encountering this problem.... it is with a fresh install of fsx with acceleration.
Whenever i hold altitude with the autopilot and run the sim at 16 x acceleration. the plane (default ones, all of them) start to oscillate up and down, up to +/-1000ft.
This does not occur at lower time acceleration, neither does it occur at low altitude (it starts at ard FL200). I do not have addons for FS, so i do not know if they are affected. This is also not a problem before i installed the acceleration pack.
Whenever i hold altitude with the autopilot and run the sim at 16 x acceleration. the plane (default ones, all of them) start to oscillate up and down, up to +/-1000ft.
This does not occur at lower time acceleration, neither does it occur at low altitude (it starts at ard FL200). I do not have addons for FS, so i do not know if they are affected. This is also not a problem before i installed the acceleration pack.