FCKEditor Text Value won't POST for some users

I've just put the FCKeditor 2.5 Beta on my site and it all seems to work great, but for some reason the text in the editor doesn't pass when some users submit the form. I've tested the editor in IE 6.0 and IE 7.0, Firefox, and Safari 3.0, and it works every single time. But it isn't working for some of the users on my site. So far they've all been using IE (6.0 or 7.0).

If you like, you can test the problem by going here, type in some text, and click submit. The text should appear just above the editor. If it doesn't, then you're experiencing the problem as well.

Any ideas on what the problem could be or how I could test it?