The ER does this as well. It is part of the FMS programming when the 1st fix is an at or above. Long story short, the plane thinks it's already on the path and will maintain the path until it needs to start down to make the restriction. I flew with the LCA who wrote the FMS book (on the ER) and he set up an artificial example just to show me this behavior. Plane slowed to about 3 knots above slats extend speed at 35k' then eventually recovered itself. Didn't descend until what should have been TOD. I have never flown the maddog so I could be talking out my butt, but this could be a case of the plane doing exactly what you told it to do. I am NOT disputing that the 88 will occasionally pull a crazy Ivan on its own accord.