Licensee has reported an issue with the source code and proposed a fix. The issue is that the source is assuming that TG_PrePhysics is the first tick group in all cases. Information can be found about the licensee's proposed fix here: https://udn.unrealengine.com/questions/279126/code-assumes-that-tg-prephysics-is-the-first-tick.html
no testing required
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-26971 in the post.