We present analysis of the mobility field dependence in disordered organic materials for the model of mixed dipolar-quadrupolar disorder. The analysis shows that the reliable separation of contributions from the different sources of disorder could be achieved only in rare cases. Additionally, we discuss the unusual dependence of the charge carrier drift mobility in molecularly doped polymers on the concentration of traps which has been observed recently. This dependence differs from the expected inverse proportionality that should be valid for trap-controlled transport. Using simulation results we argue that reason for this dependence is the faulty method of the mobility calculation from photocurrent transient. Our results also show that the mobility, estimated from the time of intersection of the asymptotes to plateau and trailing edge of photocurrent transient, is very sensitive to variation of transient shape and, in some cases, effectively masquerades real concentration and field dependence of the true mobility.