I’ve had it happen to me once on a thread, and I was copying from an email into the text box, and the person I was helping was trying to paste from word into the text box. Though one both sites, I can cut and pasted from within the site (editing the general skills for instance and copying the information from one text box to another text box in another window) without a problem. I use Firefox and Avant, and had issues on both. Might be something in the copied and pasted document you are pulling it from, I’d suggest that you try and just retype it all into the text window and not cut and paste first.
Second issue could be your connection speed. I know at times when my connection speed is so slow it tried to download the php page or just acts silly at times. Slow connection speeds cause Internet Explorer and Firefox to react to script pages oddly.