Blocks for custom user theme can't be configured if custom theme is different from default

How to reproduce the problem

1. Enable themes A and B in /admin/build/themes
2. Define A as default in /admin/build/themes
3. Go to your user settings in /user//edit and define B as your theme
4. Display /admin/build/block --> configuration for A is shown instead of B

Practically blocks for B are completely inaccessible, except you change the default theme.

How to fix the problem

Replace:

block.admin.inc, line 15:
--------------------------------------------

  // If non-default theme configuration has been selected, set the custom theme.
  $custom_theme = isset($theme) ? $theme : variable_get('theme_default', 'garland');

--------------------------------------------

With:

--------------------------------------------

  // If non-default theme configuration has been selected, set the custom theme.
  if (isset($theme))
  {
	  $custom_theme = $theme;
  }
  elseif (!isset($custom_theme))
  {
	  $custom_theme=variable_get('theme_default', 'garland');
  }

--------------------------------------------