Hello,
I think it's a bug. I have a file with babylon animation that it loads properly with ImportMesh, but when I serialize it can not recharge it with ImportMesh. I get an error:
Geometry not found for mesh dbe4c900-0ebc-41cf-8fde-052985ddb288
I have not managed to do a PG, because the file is not found, but you can compare two files and see that there are missing data in the serialized file that the file can not be recharged.
This is a file exported of 3ds max long ago:
The first file is loaded correctly : http://www.babylon.actifgames.com/bug/ok/casual01-perso.babylon
This file it after serialization is not loaded: http://www.babylon.actifgames.com/bug/casual01-perso.babylon