The best way to check if this is a graphics driver related issue or not is to uncheck "Use graphics processor" under Photoshop Edit>Preferences>Performance and then repeat the workflow. Does that make any difference on your computer?
That seems to have stopped the problem. Thanks.
Can you please advise me of the implications of this?
Does it mean my graphics processor is inadequate or faulty? (
Thanks for all that help and advice. My drivers are up-to-date. I followed the link you gave and discovered that my on-board graphics card is not supported by PS. I have a spare pcie slot so I am on the hunt for a more up-to-date graphics card - I should be able to do everything I need with what I have, but it would be nice to know that I have a compatible graphics card in my "new" machine.