Idea Notification

Hi,

We have an issue with a customer not receiving certain Idea notifications.

The customer is a Owner of an Ideas Group, and  has Ideation notification turned on on that group

, so he received a notification when there's a new Idea created, but 

doesn't receive a notification when someone comments on an Idea under that group, or changes one of the Idea's statuses.

This happens even if the customer is subscribed to an Idea by clicking on More -> Turn Idea notification on.

What could be the reason to this?