In IE or for that matter, both browsers, try experimenting with the editor's Switch Mode Button (first from left) click it once to switch from the full WYSIWYG editor to the generic Source Mode editor, click it again to switch it back. IE has had an issue with the editor for a while and Chrome may as well. As primarily a FireFox user I have to beg some ignorance as to what's going on under the hood, as FireFox just seems to work, so I lack the experience.
I can report that I have double checked your forum permissions and there is nothing that I can see that would result in the issues you are having.
I am typing this now in IE10 and when I switch the editor from source mode to WYSIWYG mode the enter key doesn't even work.
Let me know...