Steps to reproduce:

1. Log in as a user that's a member of a group with "Manage Group Filter Subscriptions" global permission (by default only "jira-developers").
2. Search for a filter, click "Subscribe".
3. In the Recipients dropdown choose "Personal Subscription".
4. In the next screen, click "Run now".

When the email is flushed from the mail queue, the following error appears in the logs:

2012-04-18 23:46:07,388 Sending mailitem com.atlassian.jira.mail.SubscriptionMailQueueItem owner: [...] /secure/admin/MailQueueAdmin.jspa [atlassian.jira.mail.SubscriptionMailQueueItem] Group 'Personal Subscription' referenced in subscription '10004' of filter '10300' does not exist.

And the user never receives the email.

If you subscribe when you're not a member of a group with "Manage Group Filter Subscriptions" global permission, everything works as expected and the subscription email is delivered.