Nate, I noticed the Editor doing goofy stuff when exporting.
Get this:
I think MeshAttachment Setup vertices are erroneously based on the vertices currently visible in the viewport.
Repro steps:
(1) Open an project with FFD.
(2) Go to Animate Mode.
(3) Pick an Animation that has FFD.
(4) Scrub to the middle of the timeline where the FFD is clearly deforming something.
(5) Export JSON.
(optional 6) Compare results with JSON exported in Setup Mode.
I guess preview these on your skeleton viewer thing?
I viewed my jsons as actual spine setups in-engine. That's where I found the bug in the first place.
1.8.25
Bug is still there. In case people are wondering.