you probably need to change the deformation order. To change the deformation order, left click and hold on the “Inputs into the Selected Object” button in the Status Line (next to the snapping toggles) and choose “All Inputs” at the bottom of the pop-up menu that appears. A List of Inputs window opens that displays all of the calculations that Maya is running as well as their order. To change the order, middle mouse click and drag an item to another position in the list.