In reply to Bendis: you can find a screenshot at
http://www.zen22109.zen.co.uk/screenshot.jpg. The white rectangle with a cross and "add or remove buttons" only becomes visible when you click the little arrows right at the end of the toolbar. This is a user-interface device normally used only when there are too many buttons to fit into the space available for the toolbar. That doesn't seem to be the case here.
I had not changed the button/toobar setup. And it looks the same on two different machines. Which is relevant to a previous suggestion that the problem is due to "non-standard" screen settings.
You see that the "add/remove" buttons option is greyed out, so I cannot remove the "ruler" button, and the "close window" button is normally hidden until you click the tiny arrows at the end of the toolbar.
Of course Karlis is right that you can do without the "close window" button. And the whole issue is not really important - except that one bit of odd behaviour in software raises questions about the reliability.
I have bought HTML-pad anyway.
best wishes,
David