Odd problems with Windows 8.1 and Internet Explorer 11

Original Goldfinch and Eagle-eye have upgraded both their computers this week to the latest Windows 8.1 and I.E. 11. Weirdly they are both unable to use the Rich Formatting option when preparing a reply to post on Forum thread pages. Is this peculiar to them, or something that the new apps do? Is there a current fix for this oddity? They both use the Loch Garten ospreys pages, especially the Weekly Chat threads.