Only when I over fill the tanks to win an economy run .The tanks hold about
another 15 litres if you slowly bit by bit fill them shake the car ,wait and
then fill them more .Maybe the pipe between the two tanks has a leak as it
happened on my wifes car and mine .
Two things come to mind - the filler neck for the tank may have
disconnected, or you may have an undetected injector leak. For the injector,
look closely at each injector - especially where the plastic bonds to the
metal - just after shutting the engine down. For the filler neck, shining a
strong light upward from under the car where the filler is and looking
inside the filler neck for light is a good place to start.