No shite... you dont say? This is from the New England Journal for Medicine, The Natl Geographic Foundation or some other scientific authority?
Good Lord, are you too lazy to Google? Try esteemed food scientist and author Shirley Corriher, who devotes space to it in her excellent "Cookwise". P 277, if you really want me to hold your hand.
Excessive heating (or reheating) of even a non-browned, starch thickened sauce will also lead to eventual thinning. Ever had a repeatedly reheated light brown gravy separate? It's starch damage. Heated for too long, the starch begins to break down and will no longer gelatinize a liquid.
Dig back into your memories of organic chemistry...or go read McGee in addition to Corriher.