Comment 2 for bug 288320

This happens because apt-setup believes that the MID install is a netboot install, and so does not create a working /etc/apt/sources.list, instead relying on choose-mirror to build one based on the preseeded mirror information. As choose-mirror is unable to download the required information from the mirror without a network, it enters a loop.

The appropriate way to fix this for the MID image is to build the image in the same manner as other images are built.

The fix for ubiquity would be to somehow trap choose-mirror's INPUT critical mirror/bad and provide the user with a graceful means to exit (either to quit the installer, or to force different behaviour in apt-setup and continue).