Race condition when you (un)subscribe

campaignmonitor_user_form() does not always reflect the correct state.

It may take a while for CampaignMonitor to register a subscription change. This means there can be a race condition when you (un)subscribe in Drupal, Drupal notifies CM but it may take a while for CM to register the change. In the meanwhile Drupal will render the "old" state.

Both CampaignMonitor->subscribe() & CampaignMonitor->unsubscribe() run
$this->removeSubscriberFromCache($listId, $email);

Instead of removing the cache, they should write it.