Flywheels/Shaft not loosing inertia

Issue description

An idle power plant shaft won't loose inertia with everything idle if powered high enough. On 5 different setups (1x HP-1MW + 2x 3MW generator + 2 Flywheel, 1x HP-1MW + 1x HP-2MW + 1x 3MW generator + 2x Flywheel (Pic2 and Pic3 idling for a game year), 4x HP-2MW + 2x LP-2MW + 4x 3MW generator + 1x Flywheel, 2x HP-2MW + 1x LP-2MW + 1x 3MW generator + without and 4x Flywheel (Pic1)). Once Shaft inertia is powered above 95% it drops to a value around 95% and sits there spinning without loosing any more inertia for several minutes. Didn't matter if the turbines power down by setting the to auto-balance or cutting steam. From a lower value or dropping the inertia below that value by activating the generator for a (split)second the inertia drops normally.

Expected behavior

Inertia of completely idle power plants loosing inertia over time.

Reproduction steps

1. Build power plant
2. Set generator to stay idle
3. Power up turbines until shaft reaches at least 95% mechanical power storage capacity
4. Idle turbines
5. Inertia initially drops to a value roughly 95% of the total capacity and stays there as long as turbines and generator stay idle

Game version

v0.4.13 (148)

This looks to still happen in 0.8.2c (b559). I have a save where two overall shafts exhibit this behavior, but trying it with a different shaft that was above 95% it was still dropping, oddly enough.