This is, essentially, a call for help, as I don't really know which program is at a fault here.
Given that Emacs's upstream converted their repository from bzr to git, all the commits in mirror repositories became "invalid" in relation to the official repository.
What does this mean in practical terms, in my case? Well, bear with me while I try to report my steps.
Noticing a regression and reporting a bug
There is a regression with Emacs 24.4 relative to 24.3, which I discovered after Emacs 24.4 became available in Debian's sid.
The regression in particular is that Emacs 24.4 doesn't seem to respect my Xresources, while 24.3 does (and this is 100% reproducible: I kept the binary packages of version 24.3 of emacs24 and I can install and reinstall things).
When I reported this to upstream, I received a reply that it worked fine with another person that was using XFCE with unstable.
Testing various Desktop environments
As I am using the MATE desktop environment, I proceeded to test this assertion by installing XFCE. Emacs 24.4 read my Xresources. I went ahead and installed LXDE. It worked again. I tried once more with GNOME 3, but "regular" GNOME 3 just crashed. I tried with GNOME 3 Classic and Emacs 24.4 just worked again.
Going deep into the rabbit's hole
Then, I got more curious and I tried to see why things worked the way that
they did and given that there was a
mirror of the Emacs repo on github, I cloned it and started
git bisect to find the first problematic commit (I have no idea if
bzr even offers something like
bisect and I wouldn't really know
how to do it as quickly as I do with
I received no response after that.
The new repo enters in action
Of course, all my hard work bisecting things was completely invalidated after the transition to the new repository went live.
To make things relevant again, I used the awesome powers of
restricting the changes of the newly cloned repository to the e-mail of the
committer in question (Chong Yidong) and, from there, I proceeded to another
painful process of git bisects.
And, sure enough, the first bad commit was the same one that I found with the previous tree.
Semi-blindly reverting this commit, and also semi-blindly resolving the conflicts make Emacs's from master work again on my system, but I highly suspect that (given the way that I did it), it would not really be appropriate for upstream.
But given also that I failed to receive feedback after my original report, I am not too confident that this bug can be solved soon (even if it doesn't qualify for being fixed in Debian 8).
After all this, I don't really know what else to do. I even filed a bug report (more like a request for help) to the Debian MATE maintainers.
As a side note, I would have filed a bug to upstream MATE, but it is not really clear what the proper procedure to report bugs to them is---they seem to use github's issues system, but given that they have separate repositories for each component of the project, and that I don't know precisely what repository to report to (or even if it applies to MATE after all), I am more or less paralyzed.
A side note
I must say that the conversion was well done by Eric Raymond, because the
.git repository of the new repo is only about 200MB, with history
going back to 1985, while the other repository had about 800GB.