Thin film photovoltaic devices based on chalcopyrite absorber layers are important candidates for the large-scale production of economically viable solar cells and modules. The material quality of the polycrystalline absorber layers is critically influenced by the bulk compositional uniformity of these films. In this regard, it has been generally reported that the structural and electronic properties of two-step processed chalcopyrite thin films are dominated by metal losses during the high temperature selenization steps. In this study, precursor films of copper and indium and/or gallium were selenized by different techniques at varying temperatures. The samples were analyzed by X-ray fluorescence (XRF) before and after each reaction step. The generally reported loss of indium and/or gallium during selenization at elevated temperatures was contradicted by XRF measurements (i.e. the amount of the metals remained constant at typical process temperatures). The apparent material losses are explained in terms of a measurement artifact of the widely used electron probe microanalysis (EPMA or EDX) due to metal segregation.