When a GByteArray is found as a function argument, it has its element-type set to guint8 by default. When one is found as a boxed object property, this doesn’t seem to happen, resulting in the following GIR XML:

    <class name="TlsCertificate"
           c:symbol-prefix="tls_certificate"
           c:type="GTlsCertificate"
           version="2.28"
           parent="GObject.Object"
           abstract="1"
           glib:type-name="GTlsCertificate"
           glib:get-type="g_tls_certificate_get_type"
           glib:type-struct="TlsCertificateClass">
      …
      <property name="certificate"
                version="2.28"
                writable="1"
                construct-only="1"
                transfer-ownership="none">
        <array name="GLib.ByteArray">
          <type name="gpointer" c:type="gpointer"/>
        </array>
      </property>
      …
    </class>

Whereas the GIR XML for a function argument of type GByteArray is:

          <parameter name="issuer_raw_dn" transfer-ownership="none">
            <array name="GLib.ByteArray" c:type="GByteArray*">
              <type name="guint8" c:type="guint8"/>
            </array>
          </parameter>

In both cases, no (element-type) annotation has been used in the source.

This may be related to bug #745001.