Thanks for the reply Phillip.
The only thing I've been able to do as a workaround is to edit the 3D
effect of the button (resize it), so that the overall border of the
button isn't so prohibitively large as to make the black box big enough
to cause the control to be grossly unattractive.
The box remains, but it's not as ugly as it once was. The control
looks slightly different now though, as it's lost some of the 3D
effect...
I do however NEED the button to be in focus, as operators like pressing
enter more than using the mouse. Can't say that I really blame
them though.