We report chemical interactions of Hf-based dielectrics with Re and Pt overlayers during annealing. Reduction of the Hf to a suboxide is observed by x-ray photoelectron spectroscopy, along with a decrease in total oxygen content measured by medium-energy ion scattering. For Re, this unanticipated reaction is highly dependent on the premetallization history of the sample. The presence of hydroxyl groups, observed by infrared absorption, is thought to be responsible. In addition, substantial electrostatic core-level shifts are observed, even in the absence of Hf reduction. The electrostatic shifts are symptomatic of altered threshold voltages for devices.