The phase behavior of a commercial phosphino-polyacrylate inhibitor (PPAA) in aqueous brine has been characterized as a function of temperature, pH, and the Ca++ and PPAA concentrations. The quantity of precipitate formed has been determined as a function of the same variables. Contrary to expectations, over a range of conditions the yield of phase-separated PPAA was found to be less than 50% and sometimes as low as 5%. Studies on a sample of isolated precipitate show that it has significant solubility even in brines with high Ca++ concentration. Ca++-induced fractionation of the polymeric inhibitor by molecular weight has been identified as the mechanism responsible for both the observed precipitation and re-dissolution behavior. The implications of these results for the optimization of precipitation squeeze treatments are discussed.