Cannot enable zoom scrolling

I am trying to enable the zoom feature by accessing System Preferences - Accessibility - Zoom and then clicking on the "Use scroll gesture with modifier keys to zoom".; however, after doing this, using Control - Scroll does nothing. When I go back into the preferences the "Use scroll ..." is NOT checked so it appears that the setting is not stored. Same problem with "Use keyboard shortcuts to zoom". In the Accessibility - General screen, the Zoom item is checked. I am using beta 3.