It seems that Android is trying to move away from this UI model. The SlidingDrawer was deprecated in API level 17 and your SlidingPaneLayout is an experimental feature. I would recommend figuring out an alternative design.
Your probably not able to see the mapview because it's really hard to draw it while the drawer is moving. The point of the SlidingPaneLayout is to help the layout of the content within a SlidingPane. This just working with spacing and moving things around. As your moving the drawer the system calls onSizeChanged and your mapview has to be redraw which is really expensive.