"Remove Unused Media" wrongly deletes External Matte clips!

I just discovered a pretty bad issue in Resolve 19.1.4, where Media Pool clips that are dragged into a node graph for use as External Mattes are not "seen" as being used in the project, even after running the "Update usage for Entire Project…" option.

This turned out to be disastrous when I created a Smart Bin to list all clips that had a Usage value of "0", from which I would select all the clips and delete them from the project. When I came back to the project a few days later, I was puzzled why many of my grades looked totally off. I eventually discovered that all of the External matte nodes I was using on the grades were all white, instead of the original matte.

I should have paid better attention to the list of Media Pool clips before I deleted them, because that's why the Matte nodes became invalidated!

Resolve should be able to track usage of Media Pool clips when they're only being used as External Matte nodes in a node graph, instead of an actual timeline clip. It can be potentially catastrophic if you have a lot of Matte nodes, and you inadvertently delete them from the Media Pool in the course of normal housekeeping.

I think this makes a lot of sense.