When I tried to save com_content setting, a JavaScript alert appeared telling me to select another component.
By researching, I found the cause of the problem. At line 43 of library.comment.php, this line appears:
array_unshift( $list, JHTML::_('select.option', '', 'com_content', 'value', 'text' ) );
I changed to
array_unshift( $list, JHTML::_('select.option', 'com_content', 'com_content', 'value', 'text' ) );
and it worked
Jaime