Keep faces together is set to on

What you are looking at in the picture is just one half of the truck, I removed the instanced ' copy for this picture

Something wierd ahppenens when I extrude the edge out that does not allow that new polygon, number one, when selected with number two, to behace correctly when I want to extrude them both to make the housing for the rocket launchers

The original polygon, number two, when selected and use a the extrude face to create two rocket launcher housings on this side, it goes way ove the x axis in to the mirrored half so I can not do it that way .... unless there is a way to deal with that