I've tried to understand what seems to be a bug in 1.11.0
Suppose you want to leave Kerbin. You plot your maneuver mode, you warp just before starting burning, you burn -> behaves like expected.
Now let's use a craft with a low TWR. We need to achieve our transfer with slowly raising your apoapsis and gain benefit of the Oberth effect for the final burn.
You plot your maneuver node. Several orbits before the maneuver node time, you start incremental burns -> the maneuver marker in the navball moves and can bounces up & down along on the pro/retrograde plane. The remaining amount of deltav to be burned varies a lot (I had 850 -> almost 5000).
Have you noticed this phenomenon?