Mixture control question

[IonicRipper]

I recently picked this game up and so far everything has been going well. One thing i'm still confused about, though, is the mixture control in the English planes:

According to the game's manual, you shouldn't exceed +1 lbs boost with the mixture set to weak. The problem is the throttle handle knocks the mixture back to rich when moved back past 50%. I heard the mixture control was fixed in the latest patch so is this a mistake in the manual? If so, what are correct settings for economy cruise?