As I predicted:

http://www.tomsguide.com/us/Windows-Blue-leak-changes-new-features-review,review-1787-6.html

As of X2A I took out the dependencies on short file names with VST's.
Perhaps the issue is with older projects saved using short file name generated ID's.
Can you confirm whether you see this on new projects or templates? (you shouldn't)

Here is an excerpt from the X2A notes regarding this:
---

Additional Installation Steps Regarding VST Plug-ins:

After installing the X2a update we recommend resetting and re-scanning your VST plugins. SONAR X2a has a new mechanism for handling file systems without short file name support. While this is not mandatory, re-scanning will allow SONAR to properly detect and handle this scenario where applicable.

This can be done by launching SONAR and doing the following:
Go to Edit > Preferences > File - VST Settings
Click the [Reset All VST Plug-ins] button 
When prompted with the message "This will reset configuration settings for all your VST Plug-ins to defaults... Are you sure you want to do this" click [Yes]
Click the [Scan VST Folders] button and wait for the scan to complete

I don't see it with new projects that I make, just the standard installed synth track templates in the Sonar content library. 

For example, inserting the first Dimension Pro track template (Dpro House Stack) I see this: 

My init file looks like this:

If you have a chance to do this - resave those templates in X2A on a machine that has 8.3 support enabled. Then load the resaved template on the system that has no 8.3 support. The new files should load OK since they will have the updated info stored.

But there are 313 files in the X2 template library and I have only this machine running Sonar.
Shouldn't the template fixes be part of an update to Sonar so that everyone doesn't have to do this?

I meant for you to try it with one template and see if it solves the issue for you.