Description:
pacman -Syu became impossible over the weekend when subsurface and digikam were installed due to a conflict (I believe) between subsurface-marble and the one digikam uses.
Now, it's not possible to have both packages installed due to file conflicts.
I removed digikam in order to do the system-wide upgrade, then tried to reinstall it, without success. After removing subsurface (and its marble) I could install digikam again, but reinstalling subsurface now yields

pacman -S subsurface
[...]
subsurface-marble: /usr/share/marble/data/weather/weather-storm-night.png exists in filesystem
subsurface-marble: /usr/share/marble/data/weather/weather-storm.png exists in filesystem
subsurface-marble: /usr/share/marble/data/weather/wind-arrows.svgz exists in filesystem
Errors occurred, no packages were upgraded.

There's a huge list of files like that, so I can't scroll back to the beginning of the list...
The errors on trying to upgrade before were similar.

Additional info:
* package version(s)
community/subsurface 4.4.2-1
community/subsurface-marble 4.4.1-1
extra/digikam 4.12.0-1
extra/libmarble4 15.08.0-1

Steps to reproduce:
See above, but
pacman -S digikam
pacman -S subsurface

or vice versa won't work.