Comment 3 for bug 367287

No problem.

The source package is different to the binary package. Some packages build many binaries. For something like clamav, a virus scanner, the following binaries are produced: clamav-base, clamav-docs, clamav-dbg, clamav, libclamav-dev, libclamav6, clamav-daemon, clamav-testfiles, clamav-freshclam, clamav-milter.

What you're searching for and installing is the binary, not the source. However, in launchpad, we go by sources. If you ran 'apt-get source kubuntu-restricted-extras', you'd find it wouldn't exist.