Our default theme is "Custom"

That's because we set the cursor theme to "Human" and the human-theme index.theme has no "CursorTheme=Human", either this line should be added or we should use the default theme and rely on the cursor theme alternative for that to be correctly configured. Reassigning to human-theme

The index.theme file for the default Human theme does have a line under [X-GNOME-Metatheme] set to CursorTheme=Human. Not sure if this is what you are talking about or not though.

I am not talking about the cursor theme; I am referring to that if the
user changes the theme, it is difficult to return to the default
(light-colored Human color theme.)

This is a completely different bug from last release. I was referring to the bug in Hardy when I filed my report. The Gutsy theme shows up in Hardy as "Human", but the Hardy default theme (lighter colors) shows up as Custom.

Actually the current Human default uses nearly the exact same colors as the previous version. Does the default for new users use the "Custom" or the "Human" theme?

The default is Custom. The thumbnail in the Appearances panel shows
it's a bit lighter (or should be; the window decorations don't seem to
match, as I reported in bug #219409.)

> The Gutsy theme shows up in Hardy as "Human"

I don't get this. Can you rephrase how exactly the two issues differ?

The new, lighter Hardy theme shown in the screenshot has disappeared
in the newest updates. Is the Gutsy theme now the Hardy default?

The default Hardy theme having changed, this bug is now obselete.