That's very interesting. My StarSan solution turns slightly milky fairly quickly (within a day), but the pH stays below 3.5 and it still foams like mad (I don't know if that's related to the surfactant or not) for several weeks.
So far, no infections.
On Deck: Jamil's Vanilla Robust Porter
Fermenting: Orange Blossom Mead
Kegs: Element 56 Pale Ale, Ron's Belgian Blonde, Summer'n Saison, Furloughktoberfest '09, Grateful Pale Ale, Sam Adams Cream Stout Clone, EdWort's Apfelwein