Don't know if has been reported already, if so i'm sorry for posting this again
Tested on BF110 C7 but probably the same on C4:
Case: Spawn with FUEL 50%
Fuel Tanks level indicator show Front Left / Front Right tanks as FULL and Rear Left / Rear Right tanks as EMPTY (correctly)
BUT, if you try to switch engine's feed from FRONT LEFT to FRONT RIGHT tank engines shutdown (if fuel tanks level indicator say right, this should keep engines running)
Otherwise, if you try to swith from FRONT LEFT to REAR LEFT engines keep running (if fuel tanks level indicator say right, this should cause engines shutdown)
S!