Menu Buttons will not forget?

[spreadz]

A Xara software owner for a good while now, but just getting around to re-doing a web design. Very early in the experience I'm puzzled, so can anyone shed light on what's going on with my menu buttons?
A big black pop-up appears behind some of the buttons when the mouse is over (when using preview and if published to the web). Weirdly the pop-ups appears to have *memory* of what the button text used to be before I amended them.
However, if I move the 7 buttons en bloc to say a central position below the proposed banner space, all appears well.

This Xara rookie is very confused.

spreadz