furbster: Fwiffo had the same problem in firefox, and I'm not sure if he has it fixed yet (using a different browser worked for him.)

Things to try:

Reload the page while holding down "shift" key - this forces the page to reload all the graphics again and hopefully the board graphics correctly.

If that does not work, try clearing the browsers cache - this also will remove all the graphics from the page making the browser to re-download the game board graphics.