At the moment there are a lot of problems with CKEditor and IE11
Many of them are listed here, but there might be local plugins that have issues.
We plan to set IE10 compatibility mode for the Sakai 10 release so this will be more of an 11 issue once IE11 is released to look at and probably involve updating plugins and CKEditor. I'm opening it as low priority at the moment just in-case anyone looks for it.
The workaround it to set the property