Update ....
It now turns out that the buttons are not "missing" per se.
They are there, but simply they fall outside of the bounds of the dialog window,
i.e. below the bottom visible border of the window,
Either the form content is being displayed too large, or the window too small !?!?
That's led me to play with my system resolution and font size ... to no avail yet.
Still .. it's a step forward I guess.
A temporary work around is to set focus on the OK button by using the TAB key .. I can now get my expressions to be submitted.
Must find a proper solution though .......