The com radio in 4.1b2 contained a bug which prevented the preset buttons from updating the com frequency. A quickfix can be downloaded here.
Replace the file “..\Airplanes\Saab_35_41b2\panel\j35bm.cab” in your installation with this updated version and reload the aircraft. The com radios will now react to both the preset buttons and the dials, as well as ATC commanded frequency changes.
The full beta download has been updated and now includes this fix.