Kerbal Space Program

Normally stable orbits are gradually changing without any force inputs, i.e. thrust, RCS or atmospheric drag. The effect does not appear to be random drifting but of steady, continuous decay of both major and minor axes at exactly identical rates in vehicles not capable of thrust, RCS and operating outside of any atmosphere, such as when one uses the cheat menu to place a vehicle into an orbit.

Of possible significance is that the effect is not consistent in 3-dimensional space, but relative to the vehicle: If a fairing is deployed in a "stable" orbit with low force, it always deploys motion-wise toward the nose of the vehicle regardless of whether the nose of the vehicle is prograde, retrograde, radial in/out, normal or anti-normal.