why subscription state is 'pending' for some nodes?

We are using Openfire 3.9.3 and our application server has smack library.

Application server is responsible to create nodes on openfire and we have this model for that:

final ConfigureForm form = new ConfigureForm(DataForm.Type.submit);

            form.setCollection("updates");

            form.setPersistentItems(true);

            form.setAccessModel(AccessModel.open);

            form.setPublishModel(PublishModel.publishers);

            form.setSubscribe(true);

            form.setNodeType(NodeType.leaf);

So, i expect openfire will not ask to our server for approval when some users want to subscribe the node.

But some users cannot get pubsub somehow and 'state' is pending on ofPubsubSubscription table for such users.

Can anyone help how subscription state can be pending even access model is open?