Hi,
mojoPortal uses CKeditor and/or TinyMCE editor. I am aware that CKeditor made a new release of their editor with some fixes for IE 11 on the same day we released mojoPortal 2.4.0.0, so it did not make into the current release.
However, we have already updated to the new version of CKeditor in our source code repository and we are very close to making a new release of mojoPortal that should fix this.
I am not able to reproduce the problem you describe using IE 11 on our demo site which is already using the new version of CKeditor. So you can check there to confirm the problem is fixed.
Best,
Joe