If you set an Event for Donations (Users who join a group) And you select the group in the event that you want to activate the event this is what happens.
Go into your Paid Subscriptions and setup a subscription that puts a user into a secondary group that was configured as the group for Donation event.
Manually add a user to the subscription, go into the site and check, you'll see you've earned your currency.
Now go back into paid subscriptions and manually add another user. Log in as him and you'll see you receive the award twice. I'm not sure what the consistency is in this but it appears to be a bug.
Go into your Paid Subscriptions and setup a subscription that puts a user into a secondary group that was configured as the group for Donation event.
Manually add a user to the subscription, go into the site and check, you'll see you've earned your currency.
Now go back into paid subscriptions and manually add another user. Log in as him and you'll see you receive the award twice. I'm not sure what the consistency is in this but it appears to be a bug.