MarshallingException when using multiple directory selection in a multi-value complex field

Edit and saving of multi-value directory selections fails under certain circumstances.

Reproduction Case
Build the project in the attached sample-27257.zip file (mvn install) and deploy the resulting target/sample-27257-core-1.0-SNAPSHOT.jar to a clean uncustomized Nuxeo instance.

The attached video shows how to do the reproduction case:

• create a File document and click the Pencil icon to edit
• add a new Source Code entry and select from the Languages vocab, click Save (No error)
• click the Pencil icon to edit again, add a new Source Code entry, click Save (Document saveError is displayed)
• Remove the new Source Code entry, click Save (Document saveError is displayed)
• Remove the first Source Code entry, click Save (No error, as there is no problem in storing an empty scg:service list)

The bundle includes an alternate Edit layout (nuxeo-file-edit-layout-alt.html) that gets deployed to nxserver/nuxeo.war/ui/document/file. If you rename it to nuxeo-file-edit-layout.html and do the same activities described above, while the data table behaves wonky in its own way, selections can be progressively saved.