Incorrect list of block regions for Slate theme

Related to #515752: Block administration not available for Slate theme, I have been trying to correct the list of available regions on the block settings for the Slate theme, but this does not currently work.

As far as I can interpret it, the blocks admin page calls system_theme_data, which re-reads all theme info files via _system_theme_data, that causes all the theme information in the system table to be rewritten. Since the Slate theme is not available the normal way, it is not detected, and is just deleted from the system table.

Its added again at a different point (not sure where, but probably triggered by some admin page), but with the default settings for many of its settings, not using the ones from slate.info. I'm a bit stumped as to what's causing this. I've tried to change _admin_init_theme to read from the .info file instead of using hardcoded values for everything (patch attached), but the theme still has the default regions listed in its data in the system table (when it is there, which is not all the time).

Makes me wonder if this theme-inside-the-module trick is really worth the trouble…

In any case, I am a bit bewildered as to how to fix this – I hope it can be made to work, because having the block system available in the admin theme will make it so much more powerful…