Maybe a bug that will go away anyway, but there's a funky link between which sites are checked, and whether the density buttons are available.
If you have no sites checked (i.e. only hits that are in 3D display are on left-side list), then if you turn on density, the relevant site gets re-selected, and the left-side list expands accordingly. (It should not.)
If you have density displayed, and then you turn off all sites, then the density buttons get inactivated.
Maybe a bug that will go away anyway, but there's a funky link between which sites are checked, and whether the density buttons are available.
If you have no sites checked (i.e. only hits that are in 3D display are on left-side list), then if you turn on density, the relevant site gets re-selected, and the left-side list expands accordingly. (It should not.)
If you have density displayed, and then you turn off all sites, then the density buttons get inactivated.