If you have encountered this issue,

for ex:- When you add custom html code  and it’s not visible in the admin and often not rendered in the front end, there is a simple hack for this.

Goto,

js\mage\adminhtml\wysiwyg\tiny_mce\setup.js

and add “extended_valid_elements : ‘i[class]'” , code to var = settings

 var settings = {
schema : ‘html5’,
mode : (mode != undefined ? mode : ‘none’),
elements : this.id,
theme : ‘advanced’,
plugins : plugins,
theme_advanced_buttons1 : magentoPlugins + ‘magentowidget,bold,italic,underline,strikethrough,|,justifyleft,justifycenter,justifyright,justifyfull,|,styleselect,formatselect,fontselect,fontsizeselect’,
theme_advanced_buttons2 : ‘cut,copy,paste,pastetext,pasteword,|,search,replace,|,bullist,numlist,|,outdent,indent,blockquote,|,undo,redo,|,link,unlink,anchor,image,cleanup,help,code,|,forecolor,backcolor’,
theme_advanced_buttons3 : ‘tablecontrols,|,hr,removeformat,visualaid,|,sub,sup,|,charmap,iespell,media,advhr,|,ltr,rtl,|,fullscreen’,
theme_advanced_buttons4 : ‘insertlayer,moveforward,movebackward,absolute,|,styleprops,|,cite,abbr,acronym,del,ins,attribs,|,visualchars,nonbreaking,pagebreak’,
theme_advanced_toolbar_location : ‘top’,
theme_advanced_toolbar_align : ‘left’,
theme_advanced_statusbar_location : ‘bottom’,
theme_advanced_resizing : true,
extended_valid_elements : ‘i[class]’,
convert_urls : false,
relative_urls : false,
content_css: this.config.content_css,
custom_popup_css: this.config.popup_css,
magentowidget_url: this.config.widget_window_url,
magentoPluginsOptions: magentoPluginsOptions,

This will resolve your issue, but remember you are editing a Magento core file. So, please extend the file using the correct method.