This problem (feature?) is not necessarily limited to reed valve engines nor is it limited to DA-50's. Both my Zenoahs, a G38 and a G26 (both converted to CH ignition) do it as well. We start smaller gas planes on stands at waist height (very convenient they are too.). You can warm them up and run them up, but when you lift the plane off the stand and tilt it to clear the restraints on the stand the engines bobble and slow down and sometimes quit. I solve the probelm with one click of throttle. Once on the ground they are fine and they cause no problems in the air. I have no idea as to the cause or the solution (there doesn't seem to be one). It just happens.