valueString not being stored

I am trying an example found in Zend Gdata Google Calendar documentation.
It seem to work and create Event, but it is not storing the valueString data.
I want to use valueString to store human readable date.

Is it some kind of bug in the framework or did I do something wrong ??
Any help or hint would be appreciated very much.

Thanx

Here is the code from documentation.

$when = $service->newWhen();
$when->startTime = "2007-12-05T14:00:00-08:00";
$when->endTime="2007-12-05T15:00:00:00-08:00";

// Specify a optional human readable value for the above date
$when->valueString = "This Afternoon";

// Apply the when property to an event
$event->when = array($when);