For 9.0 we don't have the possibility to store calendar and addressbook properties on a per-user basis and therefore we simple don't allow this for now

apps/dav/lib/caldav/calendar.php

@@ -4,6 +4,7 @@ namespace OCA\DAV\CalDAV;
 
 use OCA\DAV\DAV\Sharing\IShareable;
 use Sabre\DAV\Exception\Forbidden;
+use Sabre\DAV\PropPatch;
 
 class Calendar extends \Sabre\CalDAV\Calendar implements IShareable {
 
@@ -103,4 +104,11 @@ class Calendar extends \Sabre\CalDAV\Calendar implements IShareable {
 		}
 		parent::delete();
 	}
+
+	function propPatch(PropPatch $propPatch) {
+		if (isset($this->calendarInfo['{http://owncloud.org/ns}owner-principal'])) {
+			throw new Forbidden();
+		}
+		parent::propPatch($propPatch);
+	}
 }

apps/dav/lib/carddav/addressbook.php

@@ -23,6 +23,7 @@ namespace OCA\DAV\CardDAV;
 use OCA\DAV\DAV\Sharing\IShareable;
 use Sabre\DAV\Exception\Forbidden;
 use Sabre\DAV\Exception\NotFound;
+use Sabre\DAV\PropPatch;
 
 class AddressBook extends \Sabre\CardDAV\AddressBook implements IShareable {
 
@@ -83,14 +84,14 @@ class AddressBook extends \Sabre\CardDAV\AddressBook implements IShareable {
 		}
 
 		// add the current user
-		if (isset($this->addressBookInfo['{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}owner-principal'])) {
+		if (isset($this->addressBookInfo['{http://owncloud.org/ns}owner-principal'])) {
-			$owner = $this->addressBookInfo['{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}owner-principal'];
+			$owner = $this->addressBookInfo['{http://owncloud.org/ns}owner-principal'];
 			$acl[] = [
 					'privilege' => '{DAV:}read',
 					'principal' => $owner,
 					'protected' => true,
 				];
-			if ($this->addressBookInfo['{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}read-only']) {
+			if ($this->addressBookInfo['{http://owncloud.org/ns}read-only']) {
 				$acl[] = [
 					'privilege' => '{DAV:}write',
 					'principal' => $owner,
@@ -162,6 +163,13 @@ class AddressBook extends \Sabre\CardDAV\AddressBook implements IShareable {
 		parent::delete();
 	}
 
+	function propPatch(PropPatch $propPatch) {
+		if (isset($this->addressBookInfo['{http://owncloud.org/ns}owner-principal'])) {
+			throw new Forbidden();
+		}
+		parent::propPatch($propPatch);
+	}
+
 	public function getContactsGroups() {
 		/** @var CardDavBackend $cardDavBackend */
 		$cardDavBackend = $this->carddavBackend;

apps/dav/tests/unit/caldav/calendartest.php

@@ -23,6 +23,7 @@ namespace OCA\DAV\Tests\Unit\CalDAV;
 
 use OCA\DAV\CalDAV\CalDavBackend;
 use OCA\DAV\CalDAV\Calendar;
+use Sabre\DAV\PropPatch;
 use Test\TestCase;
 
 class CalendarTest extends TestCase {
@@ -63,4 +64,19 @@ class CalendarTest extends TestCase {
 		$c = new Calendar($backend, $calendarInfo);
 		$c->delete();
 	}
+
+	/**
+	 * @expectedException \Sabre\DAV\Exception\Forbidden
+	 */
+	public function testPropPatch() {
+		/** @var \PHPUnit_Framework_MockObject_MockObject | CalDavBackend $backend */
+		$backend = $this->getMockBuilder('OCA\DAV\CalDAV\CalDavBackend')->disableOriginalConstructor()->getMock();
+		$calendarInfo = [
+			'{http://owncloud.org/ns}owner-principal' => 'user1',
+			'principaluri' => 'user2',
+			'id' => 666
+		];
+		$c = new Calendar($backend, $calendarInfo);
+		$c->propPatch(new PropPatch([]));
+	}
 }

apps/dav/tests/unit/carddav/addressbooktest.php

@@ -23,6 +23,7 @@ namespace OCA\DAV\Tests\Unit\CardDAV;
 
 use OCA\DAV\CardDAV\AddressBook;
 use OCA\DAV\CardDAV\CardDavBackend;
+use Sabre\DAV\PropPatch;
 use Test\TestCase;
 
 class AddressBookTest extends TestCase {
@@ -61,4 +62,19 @@ class AddressBookTest extends TestCase {
 		$c = new AddressBook($backend, $calendarInfo);
 		$c->delete();
 	}
+
+	/**
+	 * @expectedException \Sabre\DAV\Exception\Forbidden
+	 */
+	public function testPropPatch() {
+		/** @var \PHPUnit_Framework_MockObject_MockObject | CardDavBackend $backend */
+		$backend = $this->getMockBuilder('OCA\DAV\CardDAV\CardDavBackend')->disableOriginalConstructor()->getMock();
+		$calendarInfo = [
+			'{http://owncloud.org/ns}owner-principal' => 'user1',
+			'principaluri' => 'user2',
+			'id' => 666
+		];
+		$c = new AddressBook($backend, $calendarInfo);
+		$c->propPatch(new PropPatch([]));
+	}
 }