BUG Compound clips render cache still not workinging

This is still a holdover bug from 14 and it's a pretty bad one. With User turned on and Color Output cache checked cache rendering begins but blue areas of the render cache quickly become red again, just like in 14.

I can report that alpha transparency of compound clips is fixed. But one of the main purpose of creating a complex compound clip is to be able to cache render it on the timeline. Not to be able to do that is a major impediment to the editing work flow.

Can confirm.
Really makes it hard to manage and preview larger sequences when compound clips make it impossible to get smooth playback