Richtext field with TinyMCE - no border attribute on html tables

Hi, 

I am using the tinyMCE Editor on richtext fields. 
So when I use the table tool of tinymce editor, I can add and edit a table as expected. 
It is also possible to set a border to the table in border-settings, but the border attribute is only added in edit mode. After saving, the border attribute is not set to my html table. 

I am using V1.2.9. 

Thanks for help. 
