We're using the API to manage all user subscriptions.
There is a "Brand" custom field, which is a multiple select value.
When user subscribes to a new brand, we use Subscribers.GetSingleSubscriber to get the current information, and merge it with the new selections.
However, sometimes Subscribers.GetSingleSubscriber returns the "Brand" as empty, even though a user has several brands selected (verified), which causes the update to wipe out all their previous selections, and only save the new brand.
I would love to provide any assistance to CM developers in debugging this, as this is a huge priority for us.
Thanks for the report - can you please contact us via support(at)campaignmonitor(dot)com with more details so our developers can investigate that with you?
I will send the email with the examples, but I think I got to the bottom of this. Sometimes the XML format returned is different - missing the anyType tax. This was also brought up in this ticket: http://www.campaignmonitor.com/forums/viewtopic.php?id=4407 but no response.
EXAMPLE (same request to GetSingleSubscriber):
Array ( [anyType] => Array ( [EmailAddress] => firstname.lastname@example.org [Name] => xxx xxx [Date] => 2010-07-20 12:57:00 [State] => Active [CustomFields] => Array ( [SubscriberCustomField] => Array (  => Array ( [Key] => BirthDate [Value] => xxx )
Array ( [EmailAddress] => email@example.com [Name] => xxx xxx [Date] => 2010-07-20 12:57:00 [State] => Active [CustomFields] => Array ( [SubscriberCustomField] => Array (  => Array ( [Key] => BirthDate [Value] => xxx )
Notice the missing anyType tag in the second response.
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