An Engine plugin with the Program module type and EnabledByDefault set to true can cause the Engine to fail to build successfully due to UHT failing. I was only able to reproduce this behavior using the attached plugin. Attempting to reproduce using a plugin that I had created was unsuccessful.
The build fails with the following messages:
The build completes successfully.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-55228 in the post.