Any breadcrumb segment is considered valid if it has a valid ancestor

When validating segments currently the only check that is done is drupal_valid_path($segment_normal_path). This function checks if the current path is valid OR it has a valid ancestor. Since the validated path isn't necessarily the $segment_normal_path, I feel this segment could still be marked as invalid after a further check.

One example of this is the configure page for the Easy breadcrumb block itself. If you go to /admin/structure/block/manage/easy_breadcrumb/easy_breadcrumb/configure
you will see this breadcrumb in the easy breadcrumb block when you enable it:
Home >> Administration >> Structure >> Blocks >> Blocks >> Blocks >> Configure block >> 'Easy Breadcrumb' block
where all 'Blocks' links go to the same parent item and 'Configure block' goes to the current page.

I've made a patch that adds an extra check. If the segment is valid, check to see which path is returned by menu_get_item($segment_normal_path) (this is the path that gets validated by drupal_valid_path) and see if this is the same path. If it's not the same path, mark the segment as invalid.

With this patch (and 'Include invalid paths alias as plain-text segments' disabled), the above path will give this breadcrumb:
Home >> Administration >> Structure >> Blocks >> 'Easy Breadcrumb' block.

Len