After creation of subdomain via CCP, event handler for 'Subdomain created' event isn't called.
The behavior was considered as internal software issue with PPA-2277 and will be fixed in future PPA updates.
As a temporary workaround you can configure required action for event 'Domain added':
- Go to PPA > System > Settings > Event Handling.
- Open Domain added (ID 8500, by the default).
- Add required action.