When changing from a project with a Timecode-based ruler to a Bars + Beats type one, it will still display the timecode options for the grid, like frames and seconds. To correctly set it back to Bars + Beats I have to go to the Project setup menu, change the Display Format to something else than Bars + Beats and then back to Bars + Beats before it allows to select those grid options.
edit: This is with the Win7 64bit version.