UE-61810 - additional details

UE-61810 is due to a bug in ExportProperties in Engine\Source\Runtime\Engine\Private\UnrealExporter.cpp: If an array has only default elements at the end, its size isn’t serialized so the importer doesn’t know about those elements.

A simple way to reproduce it is to:

  • Create a material
  • Add a Layer Blend node to it
  • Add an element to the node Layers
  • Duplicate the node: the duplicate doesn’t have that element

This issue affects all parts of the engine using the text exporter, which is used for many copy/paste.
As such, and as it doesn’t produce any error, it is likely to create lots of hidden bugs in many parts of the engine.