Forge version 0.4.8a for MC 1.19+, also observed in MC 1.16 and previous mod versions.

Parts configured to copy any root part besides the basic 6 (head, torso, limbs) fail to copy vanilla animations when using the model ingame. It copies any additional transforms, but the base vanilla pose and any vanilla animations are ignored. This extends to any armor piece, elytras, capes and any duplicated root part. Inside the editor, the feature appears to work, with parts copying a root part correctly, but once ingame it fails to follow through.