Assuming the ballast system is like that on the Mobius line, there is a manual override toggle switch on the pumps that needs to be in a certain position. If not, the ballast will fill by itself. Check your owners manual and you will find the description and location of the small toggle switch on the pump you need to reposition. Since only the front bag is filling, only one of your toggle switches is incorrectly set.
(Message edited by WakeShoe on May 28, 2007)