PEP nodes return no items when asked for all of them

As noted by Daniel Gultsch (Conversations), requesting all items from a node returns no items at all:

<iq to="xxx@igniterealtime.org" type="get"><pubsub xmlns="http://jabber.org/protocol/pubsub"><items node="eu.siacs.conversations.axolotl.bundles:798568851"/></pubsub></iq>

<iq to="yyy@igniterealtime.org/phone" from="xxx@igniterealtime.org" xmlns="jabber:client" id="fq1cn6nksr" type="result"><pubsub xmlns="http://jabber.org/protocol/pubsub"><items node="eu.siacs.conversations.axolotl.bundles:798568851" xmlns="http://jabber.org/protocol/pubsub"/></pubsub></iq>