Core system upgrade mistakenly installs non-core packages

[elieux]

$ pacman -Su mingw-w64-i686-clang
:: Starting core system upgrade...
warning: terminate other MSYS2 programs before proceeding
resolving dependencies...
looking for conflicting packages...

Packages (2) mingw-w64-i686-llvm-3.8.0-3  mingw-w64-i686-clang-3.8.0-3

Total Download Size:    55.53 MiB
Total Installed Size:  589.03 MiB

:: Proceed with installation? [Y/n]