Thank you for contacting Telerik. We have an existing ticket in our Feedback Portal that addresses an issue with Test Explorer in VS2012 not discovering Test Studio tests. This should have been fixed in the Test Studio 2012.2.1420 update. Based on your description, this is still an issue.
I've gotten reports in the past that this behavior may be related to the way the Solution is being launched in Visual Studio. How are you opening your Solution? Does this issue happen with newly created Solutions? Projects? I think the best way to confirm the behavior would be to reproduce the symptoms locally.
Please provide a copy of one of your affected solutions. Keep in mind that our ticket system only supports attachments with .zip, .rar, .ace, .jpg, .gif, .css, or .png formats. You will need to compress the .sln file before attaching it to the ticket system.
Also, a screenshot of the behavior would be extremely useful. This way, we have something that can immediately be forwarded to our QA team for further testing.
I've converted this public forum post to a private support ticket to preserve your privacy.