  We suggest that under an increase of a magnetic field a spin-ladder with
ferromagnetic legs does not pass without fail through an incommensurate phase
but possibly in a straight way turns into a fully polarized ferromagnetic
phase. The spin gap remains finite at the transition point. This scenario is
demonstrated for the special spin-ladder model with exact singlet-rung ground
state. We suppose that this kind of behavior realizes for the spin-ladder
material (5IAP)_2CuBr_4*H_2O
