Selecting actors in the Scene Outliner during a PIE session results in the EditorWorld copy of the actor being selected. This means that changes to the actor's properties don't reflect during that PIE session as they should, and are instead made to the "real" copy of the actor in the EditorWorld. This can result in accidental, destructive changes to the level being edited. The expected behavior here is that changes made to actors during PIE are ephemeral and revert once PIE ends, unless "Keep Simulation Changes" is selected to copy those changes back to the level.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-146138 in the post.