At the end of an (otherwise successful) upgrade to Fedora 10 Beta, the user is presented with a window that says "Finishing upgrade process" (or something similar). This window is apparently created by the RPM callback for package cleanup. It's supposed to have a progress bar that pulses whenever a package is cleaned up, but instead the window is created and destroyed for each package.
This will be fixed in the next build of anaconda by using a pulsing progress bar instead of a really useful one.