Not sure yet if this is my old age (!), my old machine

when I go to Render > View Options there is a flicker of the dialog and then it vanishes. If I minimise then restore the Celestia window the dialog box is there but freezes when I click OK or Cancel, needing a minimise-restore cycle to get rid of it.
However, now the really odd thing, if I have two or more views split vert or horiz then all is normal ! I can tick nightlights/orbits/whatevr and they (and the dialog) perform normally. If I delete/go back to single view it then misbehaves again

Also, just discovered it when typing up this info, when I go to look at my OpenGL version to report it, (Renderer: GeForce2 GTS/AGP/SSE ver 1.2.1) that dropdown also only behaves in split window (freezes in single window)
Any ideas where I look or what I try next ?
Not critical, just curious !
thanks,
Malcolm