Comment 8 for bug 289264

This appears to be caused by apt_check / apt_check.run().

Exchanging
            result = apt_check.run()
with
            result = (0, 0)
in /usr/bin/update-notifier-kde prevents this growth of memory usage (there's minor growing still though - according to ps).

apt_check is in /usr/lib/update-notifier/apt_check.py (from update-notifier-common).

I've quickly looked into it: it used apt_pkg, which may be causing it.

btw: a comment in update-notifier-kde says that the whole checkNewPackages may not be required in the future:
 checkNewPackages = True #kpackagekit has a new package notifier but it's broken so use this

Looks like some memory profiling is required here.