This is NOT an April Fools joke, even though it very well might be…

Once again owncloud is messing stuff up.
There’s a problem with handling groups and ownCloud with ownCloud behaving incorrectly.

If you create a group, you get back the following information:

array (
'http/1.1 204 no content' => '',
'date' => 'Mon, 01 Apr 2013 08:44:15 GMT',
'server' => 'Apache/2.2.16 (Debian)',
'x-powered-by' => 'PHP/5.3.3-7+squeeze15',
'expires' => 'Thu, 19 Nov 1981 08:52:00 GMT',
'cache-control' => 'no-store, no-cache, must-revalidate, post-check=0, pre-check=0',
'pragma' => 'no-cache',
'etag' => '1',
'set-cookie' => 'PHPSESSID=00000; path=/; HttpOnly',
'content-length' => '0',
'vary' => 'Accept-Encoding',
'content-type' => 'text/html',
)

ownCloud sends back the etag ‘1’. But when we send back the etag ‘1’ it doesn’t match anything, because internally ownCloud uses md5(vcard) as the etag.
A workaround is to set the Timeout to ‘0’ which forces RCMCardDAV to update the group vcard and thus getting the correct etag before adding new users.

UPDATE: This is logged as issue #920 and fixed in git and probably next release.