Notifications don't get sent on snippet activity

When commenting on snippets, notifications are not sent. We're using gitlab 7.13.2, and we've tested this extensively. We've also checked junk/spam folders, and they're not getting "caught". The same users testing the snippet notifications were receiving comments according to their notifications settings for issues.

We tested the following scenarios, and none of the users received notifications for any of them:

note: User A is always the snippet creator

• Snippet in public visibility project that all users have developer+ permissions on project
• user B Comments on snippet created by user A, without using any @ mentions
• user B Comments on snippet created by user A, and @ mentions them
• user C comments on snippet, uses @ targeting for users user A, user D