I have tried it on Google Chrome and Internet Explorer 11 - the spell-checker here works with both (squiggly red underline).
Your difficulty may only occur here when you post in Rich Text - changing to Plain Text may alleviate this.. don't know. Here's something that might help:
Thanks! I didn't consider that it might have something to do with the enhanced form. No reel problum, I will jist have moor missellings.