The problem was solved by locking the package. First in Synaptic by locking the package. Then in the Terminal with:
sudo apt-mark hold loki
Then again with dpkg for good measure:
echo "loki hold" | sudo dpkg --set-selections
Now I can run all Elementary updates and my LowKey Viewer works like a dream. This solution is based on this Linux Uprising ...
This is an issue not directly related to eOS, and so you are probably better off asking at other (more frequented) places, or searching those places for an answer. This post on Ask Ubuntu might be what you are looking for: https://askubuntu.com/questions/217904/unable-to-boot-into-windows-after-installing-ubuntu-how-to-fix
If that doesn't work or would take ...