Description of problem: When doing a preupgrade, after rebooting, Anaconda needed 510 MB more disk space. (This may be yet another bug that preupgrade did not know this, but it was also offering to move from i386 to 686, so this may be part of it?), anyway I switched to a console and removed 510 mb of data I wasn't using when Anaconda prompted this. I then switched back to the screen and saw "Back/Cancel", and picked Back going back to this page, Anaconda presents a page with a room for a status bar, but no test, and no status. Looking at top, Anaconda was not thinking. Thus it is not possible to correct the space problem within the installer. I restarted the computer and was able to continue the install.
anaconda no longer allows going back from this screen, so I would consider this bug closed. We're running into some really tricky situations by allowing going back here (for instance, this bug) and since anaconda doesn't really give you the opportunity to change your package set on upgrade, it doesn't make sense to allow going back.