We are facing an issue with respect to EpiServer 6 Tiny MCE editor

I have added three styles “Heading 1”, “Heading 2”, “Heading 3” in the custom Styles dropdown. In the editor content I have added a table using the editor options and trying to apply these custom styles to texts in some of the cells. I select the text in a cell, then select a style in the Styles drop down, it adds a class attribute to the parent tag of the text or sometime it creats a span tag and applies to it.  Surprisingly for some of the cells it applies properly and for some it doesn't. It looks like, if the class is applied to <p> tag, or <span> it perfectly renders in the view mode and saves properly. But if it applied to <td> tag, it doesn’t, it nither displays in the view mode, nor saves when I save and publish. 

I searched for a solution in the web, it looks like there is a bug in TinyMCE, there were few suggestions but I could not apply that. 

Do you have any idea how to fix this issue? Because it is not consistently applying, for some cells it applies to span and for some it applies to p and for some it applies to td.
Do you have any idea is this fixed with the new tinymce release? If so how to upgrate the cms editor?

Thanks for the feedback