Does it also work in IE8 correctly? I was not able to get the error to happen for me. I tried visiting a couple of the galleries that I saw on the page you linked to and did not see this result.
If I were able to reproduce the issue we would have a better chance of determining what the problem may be. Are there a set of steps that you can take to get this error to occur more consistently? Also, have you modified the gallery with any additional js code or make any changes to the existing js code?