This bug really exists but only in fresh 4.1.4 installations and of course it will appear in all furture version. vB4.1.4 does not has the file functions_wysiwyg.php in the download package. For those who upgraded to 4.1.4 without to choose "Remove unused old files", this bug is not occured.
MaryTheG(r)eek has post the solution at:
How to fix functions_wysiwyg.php errors (Article) - vBulletin.org Forum
Chris