Membership Detail report doesn't show all memberships

The Membership Detail report has a hard-coded GROUP BY statement to group by contact_id and membership_type_id. That means that if a contact has two or more memberships of the same type, only one will appear. I recognize that some parts of the code attempt to prevent this scenario, but several folks have use cases where this makes sense (Eileen recently wrote a blog post about this). However, even if this use case SHOULD be disallowed, I don't see the argument for the GROUP BY.

So no matter how you slice it, I believe this is a bug. I'd gladly patch this by removing the GroupBy function. However, someone went to the trouble of writing this code, so they must have had a reason. I'll submit a patch unless someone can tell me the use case in which it makes sense to group by these fields on this report.