I have just installed openSUSE 12.1. After installation I added the Core and Extra repositories for KDE SC 4.8 (upstream release).

Reproducible: Didn't try

Steps to Reproduce:
I expect it to be reproducible, but I haven't tried it yet.

1. Install openSUSE 12.1 - selecting KDE as desktop (language Norwegian bokmål, but I don't expect that to be of significance).
2. After installation: Add the two repositories http://download.opensuse.org/repositories/KDE:/Release:/48/openSUSE_12.1/ and http://download.opensuse.org/repositories/KDE:/Extra/KDE_Release_48_openSUSE_12.1/ and define SUSE,openSUSE and obs://build.opensuse.org/KDE as equivalent vendors (/etc/zypp/vendors.d/openSUSE-KDE.conf)
3. Update installed packages
4. Check the predefined Akonadi resources.
Actual Results:  
There are two resources for contacts and two calendar resources.

Expected Results:  
One resource for contacts and one calendar resource.

I tried to clean up my system manually and removed the additional files from $HOME/.kde4/share/config/ (akonadi_contacts_resource_1rc and akonadi_ical_resource_1rc) and $HOME/.config/akonadi (agent_config_akonadi_contacts_resource_1 and agent_config_akonadi_contacts_resource_1_changes.dat and agent_config_akonadi_ical_resource_1 and agent_config_akonadi_ical_resource_1_changes.dat) and edited $HOME/.config/akonadi/agentsrc

That did not solve my problem. What it did was remove the resources which are displayed when looking at Akonadi resources (kcmshell4 kcm_akonadi), but the collections remain in the database. They are visible in akonadiconsole, but more importantly two collections are displayed when I chose an Akonadi resource as standard KDE resource for calendar or contacts.

Update:
While creating this bug report I tried to recreate the files I had deleted to see if the resources would show up again, hoping that it would let me remove the resources and that the collections would be removed along with them.
I had to manually add the resource in the Akonadi resource overview, but after deleting this the collections are now gone.

So, there is a workaround for the problem, but I am submitting this bug report anyway, as the duplicate entries should not have been created in the first place.