I tried that too, but pamac shown the warning. Did it happen because I tried with only one of them?
Anyway, I tried again.
EDIT ---- 
Yeah. I installed all packages at once and it seems work OK.
I did:
sudo pacman -Rdd user-manager-git
and then
pacman -S attica karchive kauth kbookmarks kcodecs kcompletion kconfig kconfigwidgets kcoreaddons kcrash kdbusaddons kglobalaccel kguiaddons ki18n kiconthemes kio kitemviews kjobwidgets knotifications kwidgetsaddons kwindowsystem kxmlgui solid sonnet
A difference from pacman to Pamac:
pacman warned me that removing kio-git would break the dependency with user-manager-git.
I should therefore have removed the latter at first.
Then, I had to confirm every remove operation for all items.
Pamac, however, advised that it proceeded to remove user-manager-git before removing the other packages and did it.
Only one confirm at the beginning.
We can say that pacman is more conservative and never does anything without the user explicitly asking.
In our case, the less experienced user does not know how to proceed because it does not ask to remove, but only warns.
Pamac, on the other hand, realized that user-manager-git should have been removed and did it himself.
A small difference, which however personally make me prefer pacman. 