The substitutes to install Calibre 5.36 updated, so I gave it a try today. The issue exists there too, suggesting further that the problem is in the dependencies somewhere. I haven't come across a working revision with Calibre 5.14 in my bisecting expeditions yet, but I suspect some of those would be broken in the same way.
Bisecting the branch which used to be core-updates-frozen with --first-parent has so far been fruitless. I seem to be jumping dates and Calibre versions again, and my Git-fu isn't strong enough to narrow the range of commits I'm bisecting. Many of the commits from core-updates-frozen also appear to be unbuildable; I'm not sure if that's expected, my guix-daemon being too new, or something else. I'm looking at merges *from* master into core-updates and core-updates-frozen pre-6dffce as potential problem sites. Based on the diff between the working and broken parents of 6dffce, my hunch is that the regression lies in a dependency (likely something on the Qt side) as opposed to the Calibre recipe itself.
