The KDE bugzilla hosts a range of packages that are upstream to Kubuntu including the KDE desktop and most KDE applications.
Using the bug tracker
KDE bugs are tracked upstream at bugs.kde.org. Click 'New Account' in the bottom right corner and enter your email address.
Filing new bugs
After searching for possible duplicates you can file a new bug using the guided bug filing. Include a basic description of the problem, including all relevant information in the Launchpad report, and link to the original Launchpad report:
TBD. stock text and example
On Launchpad, click "Also affects project" in the left column on the bug page, and link to the KDE bugzilla bug.
Tags and conventions