Unfortunatly this fix is only partial and on some builds of IE is not working at all. Hopefully IE6 will die out soon, and people will either use some normal browser like Opera or Firefox or they will switch to newer IE7 or IE8. Every new thing for web has problems working on IE6.
The only sure way to avoid this problem is to use gif icon sets instead of PNG. Selection of gif sets is available on the plugin website. Also there is a tutorial on how to make more sets on the wbesite and in the user guide.
There is a tutorial about adding new stars set on the website. If you add set into plugin folder, when plugin is updated, you will loose additional sets. So I set up another location for additional sets that will be safe from upgrade. Detailed instructions are in that turorial.