Cannot reorder some art with SDK

I have a plugin that creates path art and arranges it in layers, which are sometimes nested in other layers. There are a couple of items, a compound path and a group, that stubbornly do not want to be reordered.

sAIArt->ReorderArt(art, kPlaceInsideOnTop, group) does not return an error, but it does not reorder the art, either.

Doing sAIArt->ReorderArt(art, kPlaceAboveAll) before that does not help. I've tried syncing the document, to no avail.

Is there anything I can do, or any known condition where ReorderArt won't work?