rdf4j: Adding a Model to a repository doesn't transfer its namespaces

When adding a Model to a Repository with conn.add(model), its namespaces get lost. Writing the repo to a file like

RDFWriter writer = Rio.createWriter(RDFFormat.TURTLE, outputStream);
conn.export(writer);

produces a very unreadable Turtle file with no prefixes.

Only after manually re-adding them like this

for (Namespace ns : ontologyNamespaces) {
    conn.setNamespace(ns.getPrefix(), ns.getName());
}

does the output actually contain prefixes. It definitely the act of adding the model and not the RDFwriter’s fault.

If this is a bug, I’d be happy to contribute. If this is expected behavior (which is counter-intuitive in my opinion), is there a nicer way to include the namespaces when importing?

VERSION: 3.4.4