When using gridFS, expiration time (ttl) set by client application works for documents in metadata collection but does not work in chunks collection

When using gridFS, expiration time (ttl) set by client application works for documents in metadata collection but does not work in chunks collection. This results in chunks not getting cleaned up from the mongodb. However when we do delete operation, both meta data and chunks gets deleted as expected. Can you please confirm if ttl-expiration time is supposed to work with chunks ? (apparently it does not in our testing).