  We consider a model of relativistic three-body scattering with a bound state
in the two-body sub-channel. We show that the na\"ive K-matrix type
parametrization, here referred to as the B-matrix, has nonphysical
singularities near the physical region. We show how to eliminate such
singularities by using dispersion relations and also show how to reproduce
unitarity relations by taking into account all relevant open channels.
