Kerbal Space Program

When "Prop. Requirement Met" is not 100%, then the main Fuel Resource usage number does not match the fuel usage of the engine.
The first image shows fuel usage on a plane with a small intake, that is not providing enough air. Prop requirement is about 80%, and the Fuel usage number (0.15 - taking rounding into account) is about 20% higher than the engine is showing for usage (.11868).
The second shows a similar plane under similar conditions with a large air intake and 100% Prop Requirement Met -- and the two numbers match (within rounding).
The savegame (career mode) is the plane that demonstrates the problem. There are many points in its high-speed/high-altitude flight envelope where Prop Requirement met drops below 100%.

I think the bug may actually cause your fuel to drain faster than it should.