Deviation of fitting to simulated bulge r-band magnitude m_r,B,sim − m_r,B,fit as a function of the faintness of the bulge for objects with m_r < 19.8. Top: multi-band fit, mode M. Bottom: single-band fit, mode S1. The fainter a bulge within a given disk, the harder it is to fit. Red horizontal lines show a (empirically chosen) allowed deviation of ± 0. 5mags. The systematic trend reaches this limit when the bulge is ~1.5 mag fainter than the disk. Red numbers in the top-left corner indicate the numbers and fraction of objects with deviations larger than 0.5 mag above (top number) and below (lower number).