Since August 21, all the emails I received with the edits for my subscriptions are lumped together in the same thread by GMail.
Similar emails I receive from other projects are not bundled together.
I think the problem lies in the new "References" and "In-Reply-To" headers. In my case they are both set to subscriptions-319148@... Together with the same Subject header they confuse GMail into thinking of them as a single thread.
- Use an ignored email address extension in the References and In-Reply-To headers: subscriptions-319148+d20120821@...;
- Add a date to the email subject "Edits for your subscription (for 2012-08-21)".