prop=pageprops formerly added all the page properties to the page node.
For example,
<page pageid="25970423" ns="0" title="IPad"
defaultsort="Ipad"
displaytitle="iPad">
In bug 27479,[1] it was pointed out this can cause API errors if the
name of a page property conflicts with a property or node generated by
another module; for example, both prop=info&inprop=displaytitle and
prop=pageprops will try to add displaytitle to the page node.
In r82312[2] the output of pageprops was changed to place the properties
on a subnode named "pageprops" to avoid such conflicts, in much the same
way that prop=categoryinfo works. For example,
<page pageid="25970423" ns="0" title="IPad">
<pageprops defaultsort="Ipad" displaytitle="iPad" />
</page>
This is tagged for backporting to 1.17 and 1.17wmf1, although I couldn't
say when that might be done.
[1]
https://bugzilla.wikimedia.org/show_bug.cgi?id=27479
[2]
http://www.mediawiki.org/wiki/Special:Code/MediaWiki/82312