Isostatic rebound is a well known phenomena. It occurs on continental kratons that were compressed into the lithosphere by the great weight of ice upon them. Continents have a lower density due to their being made up primarily of granitic rocks which have a much lower density then the basaltic rocks that make up the ocean floors. The ocean floors are not "expanding", the ocean floors are static due to the aformentioned density differences and the fact that the ocean basins are under quadrillions of tons of water. They are NOT expanding and until the water is removed from them can NEVER expand.
The CU Sea Level Research group disagrees with you.
Why do you think the Glacial Isostatic Adjustment is made?