fallen eagle - apparently it has something to do with the venting system. There are two reasons why the fuel in a high wing Cessna flows to the engine. The first is gravity, the second is a slight positive pressure. Most Cessna high wings achieve this pressure through the L shaped vent on the left wing. The pressure should be even in both tanks. In order to make sure that it is even (apparently bad things happen if it isn't) Cessna 'link' the top of both tanks from a point at the top of the fuel tanks (Inboard). Because many Cessna tanks are loing and thin (Some 182 LR tanks are about 8 inches high but 7 foot long)and because the wing has some dihedral the equalising vent can be full of fuel rather than air. So - the right tank happens to be feeding the engine, the pressure comes from the left tank which pushes fuel rather than air through the pipes, the right tank remains and indicates full, while the left tank appears to be emptying. Worry not, this situation resolves itself when the left tank empties enough for the connecting vent not to be immersed in fuel.
Hope that helps
Ian
PS The above is sort of a precis from a six page document that the Cessna Pilot Association have put out.