FWIW...
Recently I have had 2 customers commenting on this "Save Normal Template" message appearing. One using Office 2010 the other 2013. Both were using one of my add-ins to Word that does have a "dotx" formatting template, which under the control of the VSTO
add-in, does update its Styles. The user's Normal template is not accessed or updated by our program and is not attached to any documents that we use.
During investigation I found that the user's IT department had unwittingly moved the Normal template. One had placed it on a shared Network drive and the other had placed it into the "Read Only" Microsoft Office Templates folder in the Program Files directory
on the "C" drive.
The remedy for eliminating the Save Normal Template message was for us to simply move our template out of the User Template directory and place it into another directory within the user's App Data\Roaming path. By default the User Template directory is
~\AppData\Roaming\Microsoft\Templates and this is also the default home for the Normal.dotm template.
Conclusion... if Word's Normal template has been moved out of the expected /default user template directory and custom user templates are contained within the default user template directory this can cause erroneous messages concerning saving the Normal
template when updates to the custom templates are performed.