Language page crashes in only-installable mode

Binary package hint: ubiquity

This is an oem install that included a preseed for showing only the installable languages on the oem page. I'm finding that if the apt cache hasn't been loaded before the page gets loaded, it will crash.

The attached logs show that crash.

This can also be reproduced with this simple python script if the apt cache hasn't yet been loaded:
import sys
sys.path.insert(0, '/usr/lib/ubiquity')
from ubiquity import misc
misc.drop_privileges()
import apt
apt.cache.Cache()

This is the (cropped) return from that script:
  File "/usr/lib/python2.6/dist-packages/apt/cache.py", line 88, in __init__
    self.open(progress)
  File "/usr/lib/python2.6/dist-packages/apt/cache.py", line 126, in open
    self._cache = apt_pkg.Cache(progress)
SystemError: E:Could not open file /var/cache/apt/pkgcache.bin - open (13: Permission denied), E:Failed to truncate file - ftruncate (9: Bad file descriptor), E:The package lists or status file could not be parsed or opened.

Making a minor modification, it will work however:
import sys
sys.path.insert(0, '/usr/lib/ubiquity')
from ubiquity import misc
misc.drop_all_privileges()
import apt
apt.cache.Cache()

drop_privileges is applied to ubiquity when first loaded, so it's effective on all pages. The primary difference between those two methods is that drop_all_privileges will set the euid/egid as well as real uid/gid while drop_privileges only sets the euid/egid.

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: ubiquity 2.4.1
ProcVersionSignature: Ubuntu 2.6.35-22.33-generic 2.6.35.4
Uname: Linux 2.6.35-22-generic i686
Architecture: i386
Date: Sat Sep 25 22:32:08 2010
DistributionChannelDescriptor:
 # This is a distribution channel descriptor
 # For more information see http://wiki.ubuntu.com/DistributionChannelDescriptor
 canonical-oem-dell-maverick-une-20100925-0
InstallationMedia: Ubuntu 10.10 "Maverick" - Build i386 LIVE Binary 20100925-01:44
ProcEnviron:
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ubiquity