There is a bug here or maybe i'm using the gem wrong...

edit: this is a new version 

You should merge the ACLs after merging the meta_hash if not the new permission will be overwritten by the old one.
If Before you had a directory with :
X-Container-Read: .r:*,.rlistings

and you make your directory private again. The new read_acl will be overwritten by the old one in the mata_hash

Normally i think that first you should merge the default/previous options and then you apply the new ones and at the end you apply the user specified options if there is any