Agreed. Your engine is trying to compensate the fuel ratio and timing to deal with engine operating conditions. So either you have some mods that are allowing the engine to breath better (and hence use more fuel), or if your engine is all standard then it's related to a fault such as an intake or exhaust leak. I believe it can also be related to running a standard engine up to the fuel cutoff point (i.e. red line), though I have no direct experience there.
