Contax 159mm Aperture readout problem.

I have revived a Contax 159mm by cleaning the release magnets only to bump into a new problem. When in have my 50mm/1.4 mounted and stop down 1/2 stop at the time, the Aperture readout is correct until stopped down to 4.0. After that when I stop down further towards 16, the readout display goes up to 3.5, 2.8, 2.0 and 1.4 again. Does anyone know what would be causing this?