I could be wrong, but I have the feeling that after baking chocolate chip cookies, the chocolate chips are still melted; or at least a lot softer than before you bake the cookies.  It's logical that the chips melt, when they are in the oven, and even half an hour later. But why are they still softer the day after? What's the explanation behind this? It's as if the melting point has lowered.  Or am I imagining things? 
Chocolate is in is most essential form made up of cocoa butter and cocoa solids. The chocolate you buy is tempered, the crystals in the cocoa butter are aligned and properly formed, this is what keeps it shiny and gives it a snap.  When the chocolate melts, without tempering, in the cookie the crystals in the cocoa butter melt but do not form properly again, this means the chocolate becomes soft, dull and 'blooms' fat which is where the cocoa butter rises to the surfaces forming a white layer (this will disappear upon melting).  Also in a cookie there will be a high proportion of fat and when the chocolate melts it combines with the fats (in the butter) and will create essentially pockets of chocolate glaze, which obviously doesn't set hard. 