Yes, it happened to me on IE8, they were all gone. All you have to do is refresh the page.
Another issue I've found with browsers is that when adding certain custom markers the entire page goes blank, this happens rarely and it looks like it is a cache issue with google maps. I delete my browser cache and it all comes up fine.
There is another issue with IE9 in that longer member names show out of the box when you click on them, all you have to tell your users is to use compatibility mode on IE9 and the member names will show up fine. IE8 and the rest of the browsers don't have this issue.