I think the issue is probably that some of the abstract pieces are smaller than the square size.
Indeed, the Abstract images have variable size. The movepiece.js script copies their URL from cell content to background style, and apparently the default mode for background is to tile, starting in the upper-left corner.
This was easy to fix: in the loop that does the image copy I now also set the background-repeat and background-position styles to 'no repeat' and 'center center'. You would probably have to append a ?nocache=true parameter to the movepiece.js URL to make sure the new version is used.
Indeed, the Abstract images have variable size. The movepiece.js script copies their URL from cell content to background style, and apparently the default mode for background is to tile, starting in the upper-left corner.
This was easy to fix: in the loop that does the image copy I now also set the background-repeat and background-position styles to 'no repeat' and 'center center'. You would probably have to append a ?nocache=true parameter to the movepiece.js URL to make sure the new version is used.