We present the results of measuring transverse conductivity alpha(perpendicular toc) of bipolar heterogeneous semiconductors in classical strong magnetic fields. A stochastic distribution of current carriers (electrons and holes) was created by interband illumination through special masks. The main parameters of crystalline p-Si:13 placed in liquid He were the concentrations of the main and compensating impurities, 7 X 10(15) and 4 X 10(12) cm(-3), respectively; and the mobilities of electrons and holes, 1 X 10(6) and 5 X 10(4) cm(2)/V s, respectively. An anomaly in alpha(perpendicular toc) was observed: the ratio of alpha(perpendicular toc) for heterogeneous and homogeneous samples depended on magnetic field in a nonmonotonic way, i.e., alternation of increasing and decreasing regions of relative alpha(perpendicular toc) for H=0-10 kGs and monotonic growth for H=10-40 kGs. To explain this effect, a theory is presented which is a development of the alpha(perpendicular toc) theory for heterogeneous semiconductors with one kind of carrier. It is shown that the effect is due to the redistribution of roles of electrons and holes in magnetoconductivity of homogeneous semiconductors. This effect has high sensitivity to degree of disorder and can be used for detection of small irregularities and as a diagnostic of semiconductor purity.