Zend GData Calendar: I can't use setUpdatedMin in the query

Question

I am trying to get all the events created on Google Calendar after a timestamp (let's say one hour ago).
I am using the Zend GData library.

If I run this code (after the initializations needed) everything works perfectly:

$query = $this->service->newEventQuery();
$query->setUser($this->getCalendarId());
$query->setVisibility('private');
$query->setProjection('full');
$query->setOrderby('starttime');
$query->setSingleevents('false');
$query->setParam('ctz', 'UTC');
$query->setMaxResults(5000);

// Retrieve the event list from the calendar server
try {
    $eventFeed = $this->service->getCalendarEventFeed($query);
} catch (Zend_Gdata_App_Exception $e) {
    echo "Error: " . $e->getMessage();
}

But when I try to set the updated-min parameter of the query in this fashion:

$dateFormat = 'Y-m-d\TH:i:s\Z';
$query->setUpdatedMin(date($dateFormat, time()-3600));

I get this error:

Unknown authorization header
Error 401

Then, I found out something very interesting debugging the Zend Gdata library: the url that gets sent off to Google is this:

http://www.google.com:80/calendar/feeds/mywebsite.com_f7j5nudhqc8p7suju8svd2gl8s@group.calendar.google.com/private/full?orderby=starttime&singleevents=false&ctz=UTC&max-results=5000&updated-min=2011-03-14T15:17:37Z

If I turn it into this (I have only changed http:// to https://)

https://www.google.com/calendar/feeds/mywebsite.com_f7j5nudhqc8p7suju8svd2gl8s@group.calendar.google.com/private/full?orderby=starttime&singleevents=false&ctz=UTC&max-results=5000&updated-min=2011-03-14T15:17:37Z

and paste that URL in Google Chrome I get all the events updated after 2011-03-14T15:17:37Z, as I wanted.

Based on that, I thought it would be a good idea to change the content of the $scope variable in the initialization code to generate the URL for the user authentication:

$next = getCurrentUrl();
$scope = "http://www.google.com/calendar/feeds";
$secure = true;
$session = true;

// Redirect the user to the AuthSub server to sign in

$authSubUrl = Zend_Gdata_AuthSub::getAuthSubTokenUri($next,
                                                     $scope,
                                                     $secure,
                                                     $session);

from

$scope = "http://www.google.com/calendar/feeds";

to

$scope = "https://www.google.com/calendar/feeds/";

(as documented here http://code.google.com/apis/calendar/data/1.0/developers_guide_php.html)

But in that case, I get:

Token invalid - AuthSub token has wrong scope

I have run out of ideas after 10 hours of debugging and googling! I don't know what to do. Please any ideas or workaround is very welcome.

Thanks,
Dan