WordPress problem with htmlentities

It seems that the “convert_chars” filter is causing the trouble, try removing it by:

remove_filter( 'the_content', 'convert_chars' );

Also try removing the richedit_pre hook (which formats the text for the rich text editor, also uses convert_chars function) by:

remove_filter( 'the_editor_content', 'wp_richedit_pre' );

Hope that helps!