Can't change fuel below 60%

[coldViPer]

Sorry if this is asked before but why I can't change fuel amount below 60% in campaign mode? Known bug? In quick mission I can set 10% minium. At the moment I fly only HE-111 and 60% fuel is way too heavy 

[312_Tygr]

It's a feature, preventing you from starting a mission with too little fuel to finish it. I guess it could do with some tweaking, I usually have too much in La-5.