Properties are not being persisted when document only extends hippo:document and does not have the property in prototype

Suppose you have :

[demosite:textpagenew] > hippo:document

• demosite:title

thus not extending hippostd:publishable, hippostd:publishableSummary.

When the prototype has:

<sv:property sv:name="demosite:title" sv:type="String">
<sv:value/>
</sv:property>

then when editing a newly created document works correctly with respect to saving. When the prototype does not contain <sv:property sv:name="demosite:title" sv:type="String">, then, the BE template is shown correctly, but after editing the title field, and clicking on save, the changes have not been persisted