None of the usual experts seem to want to answer this.
In THEORY, when you lean the mixture without any change in throttle setting, the fuel flow will always decrease. In practice, if when leaning you cause power to increase and there is a momentary increase in RPM as a result, I suppose it is possible for the engine to draw in more fuel which could show as an increase in fuel flow. But I would expect any such increase to be momentary, because unless the propeller is on the fine pitch stops it will govern back to the selected RPM.
A fixed pitch propeller installation (unlikely in a turbo) could possibly behave somewhat as you describe - I dunno because I have never flown a fixed pitch prop turbo charged engine, and never tried to run a turbo engine above max power altitude in full fine pitch.
Over to the experts now......
Last edited by Mach E Avelli; 6th Nov 2013 at 07:42.