Lots more info in UDN ticket: [Link Removed]
TLDR is that if a construction script moves a child component with an attachment point, it's attached actors don't follow. This causes editor tools to not work because changing default variables calls the construction script
Unfortunately reproducing this bug is quite cumbersome. Contact @jordan.hoffmann and I'll give you a scene you can use to reproduce it
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-161232 in the post.