IMHO, these should all have the same titles, so they are threaded in email clients cleanly.

That's not a problem since we use email-id and in-reply-to and email clients rely on this first and if absent consider the titles.
Are your emails not sorted by PR/issues? They certainly are for me :)

Yeah, i'm using gmail, and it seems it relies pretty heavily on the subject line to dermine threading. :(

http://webapps.stackexchange.com/questions/965/how-does-gmail-decide-to-thread-email-messages

Sucky gmail, I'm really pondering here :-s I like the subject to reflect info about the content, but being nice to gmail users might also be nice.

It might make more sense to open an issue with gmail for their web interface. Do they they really get much mail with reused in-reply-to or references headers that shouldn't be linked?
It seems wrong to make things less useful because gmail breaks threads when the subject changes.

it seems that it is a long-standing issue with gmail threading -- i really don't like the chances of getting it changed.

I notice that a lot of other services that deliver email, just do so with the same subject header (with "Re:" prepended for replies).

The real question here is if the value of having different subject lines is worth breaking threading for people that use gmail.

Supposedly a lot of people don't like they way gmail does threading and turn it off. So this change would only help the people who leave it on and use the web interface. That's probably still a fair number of people.
If there is spare development time, maybe there could be a per person setting to make gmail friendly messages.

Fixed by @ryanlerch in: https://pagure.io/pagure/pull-request/1009