Applying Active Layer Resets Lower Layer Cache

This has been a bug with layer stacks since they were released in v19 and it still hasn't been fixed.
Details are in this thread:
https://forum.blackmagicdesign.com/viewtopic.php?f=21&t=211345
Details are in this thread:
https://forum.blackmagicdesign.com/viewtopic.php?f=21&t=211345