When a user removes a submission by his group to an assignment (referring to mod_assign), no event is triggered and thus no log entry is generated. This is due to this line in the remove_submission method, which triggers the submission_status_updated event, if the user ID of the submission is nonzero. In a group submission the user ID is zero; there is only a group ID. Unfortunately that if-statement is not followed by any logic that triggers a corresponding event, when the submission was made by a group. The method simply exits.

I consider this a bug, and a serious one at that. The log shows removal of (user) submissions for good reason. That way a student cannot claim that his submission simply "disappeared", after he received confirmation of his submission. Failing to show this event in the log, simply because it is a group submission makes no sense. It is still a user (from that group or otherwise) that actively removes a submission. This must be logged.

We just spent an entire day trying to figure out, why a submission seemingly "vanished" before realizing that it was, in fact, removed by a group participant, since the Moodle log did not show this event and the webserver access logs merely provided clues. This is not to nag, just to underscore why this is a serious problem.

The solution should simply be to trigger an event when a group submission is removed.