Wubi, Ubuntu 9.10 AMD64, 30G installation size, grub prompt

I have detected an unusual edge case. If I try to install Ubuntu 9.10 for AMD64, and set the installation size to 30G I end up with only seeing the grub prompt when I finally get to the stage of booting Ubuntu (IE: after the installer is finished after rebooting the first time).

If I cat the grub.cfg file I only see <0>'s (nulls).

If I set the installation size to 29G or below, Ubuntu boots perfectly.

If I use 32 bit Ubuntu instead of the amd64 version, Ubuntu boots perfectly.

I tried reinstalling multiple times and it consistently worked for sizes 29G and below, and consistently failed setting to 30G.

Note: I'm not keeping this Windows installation, and thus can't do ongoing diagnostics. It came pre-installed on a machine I intend to wipe and install Ubuntu on the entire disk. I only wanted to see how Wubi worked, and ended up noticing this problem as my first attempt involved setting the installation size to the maximum the pulldown allowed.