1. Create a Blueprint class with a parent of PrimaryDataAsset
2. Make a structure
3. Make the member a Map.
4. Set the Value of the Map to the 1 (object reference)
5. restart editor
result : the value of 4 is changed to PLACEHOLDER-CLASS
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-155281 in the post.