I'm not the developer of CKeditor so any bugs with CKeditor should be reported to the CKeditor site. We always ship the latest version of CKeditor with mojoPortal but if you upgrade to a newer mojoPortal the old version of CKeditor is still on disk and you could configure it to use an older version from Web.config if you find the problem doesn't happen in an older version of CKeditor.
Only thing I can think of to recommend trying is maybe disable the spell check as you type feature, it may be a factor. See this thread for notes how to do that.
Hope it helps,
Joe