Magneto-resistance measurements in narrow single quantum wells show very sharp (width ≈0.2 T) maxima at fractional filling factors between 1 and Image . The peak values of the new maxima exceed the resistance values in the surrounding magnetic field region by a factor of up to 3. The formation of the maxima is hysteretic and takes place on a long time scale. This points towards a close relation with the nuclear spins. Those new maxima will be discussed in the framework of domains having two different spin ground states.