This is more of an FYI for the general community than an actual bug.
After UP4, Brasero no longer wanted to properly burn data DVDs for me. It would go through the motions, and it looked like it actually burned something to a blank DVD, but the DVDs (which were DVD-Rs) were unreadable. I ended up installing xfburn, and that works properly, so that was the fix.
I think this is related to the fact that UP4 seems to have applied a Nautilus update to my machine. I didn't even realize that I had Nautilus, but I'm thinking that parts of it were installed by virtue of all the various gnome-related bits (chiefly gdm3, but there was probably more). As I detailed in another thread, whatever the reason it switched my default filemanager from Thunar to Nautilus and hijacked my desktop settings, even after I'd removed the Nautilus package entirely. I ended up doing a much-needed rebuild of my home directly to remove the accumulated cruft of several years worth of various conflicting desktop settings (I had been copying my /home directory from distro to distro as I moved to them), but at least I won't have to wipe and install.