Right Tip fuel got used?

I've never noticed this before...but that doesn't mean anything :-lol . On a recent multi-leg flight I flew to Split (LDSP) to refuel and wait. It was while looking at the FS9 fuel window, to refuel, that I noticed that the 6.70 pounds of fuel in the Right Tip tank was gone. Is this a problem? I couldn't get "6.70 lbs." to load in the Right Tip (the usual "select a number between 0 and 6.70" message), so I selected the default Cessna then re-selected the USAFE TM2 I am flying, to get it back to 6.70 lbs.So, should I be concerned about losing fuel in the right tip ( I understand why it, the tank, is there...to distinguish between models)? Thanks! Vic