Bug 384907

Going to Configuration>Configure Sources and selecting the "+" option let me add a repository, but it won't really add it, as it doesn't appear on the list. Selecting Configure Software Sources asks for root, ok. At the Kubuntu Tab all sources are selected, except Source code, Download from Main Server (did try other servers and got same result). In Other Software Tab, added the following repos:
deb http://archive.ubuntu.com/ubuntu $(lsb_release -sc) main universe restricted multiverse
deb http://archive.canonical.com/ubuntu $(lsb_release -sc) partner

Selected Check for Updates, and nothing changed (Steam, LBreaker2 and some other softwares couldn't be found and the repository list in software management didn't change).
Did sudo apt-get update and upgrade, but the list didn't include the repos I added.

On terminal added trough apt-add-repository, updated, it worked on terminal, the new repositories were found and updated, but Discover still can't find the software and the repositories doesn't appear on the list.

Trough apt-get I did install the software I wanted, and surprisingly, it appeared on Discover Package History.