This problem seems to be isolated to Safari on a Mac.
I have viewed your galleries in Safari 5.1.7, Chrome 31, Firefox 26.0, IE11 and Opera 18 on a PC and all galleries I have tried expanding work fine in all browsers.
First of all, try clearing your browser's cache before reloading your web page to ensure that your browser is fetching and using the most recent files from your web server.
If this does not help, then try setting expandInNewPage="TRUE" in your gallery configuration options.
Please see here for more details about the expandInNewPage configuration option.
You could also try changing useFullscreenExpand from 'TRUE' to 'FALSE' to see if this makes a difference.
I realise that you may not want to change the value of this configuration option permanently but it may help to troubleshoot the problem.