I'm not sure whether this is an error in the media-sound/amarok-utils-2.3.1 or media-sound/amarok-2.3.1-r2 ebuilds, or if they are fine and there is a bug in paludis (0.52.3). Anyway, I will first try it here, and I will be happy to report this as a paludis bug as well.
amarok blocks amarok-utils. Maybe there is a good reason for that if you want to build amarok, but it also makes any attempt to update world fail, even if amarok would not be built in the course of that world update.
Steps to Reproduce:
1. have media-sound/amarok-2.3.1 and media-sound/amarok-2.3.1-r2 installed
2. update world
3. fails because amarok blocks amarok-utils
4. Workaround: uninstall amarok-utils without removing it from world (paludis --preserve-world), then update world
amarok and amarok-utils ebuilds have been merged in amarok-2.3.1-r2. So you need USE="utils player" to have them both installed. Portage should autoresolve the block, I don't know how paludis should handle it though. Closing as invalid. Thanks
I see – thanks for your help! I wasn't aware of the merger. I have these use flags for amarok, so I guess the problem will be solved by simply uninstalling amarok-utils.