--- modules/block/block.module.614.orig	2008-06-24 15:40:08.000000000 +0100
+++ modules/block/block.module	2009-09-22 17:24:59.000000000 +0100
@@ -257,6 +257,20 @@ function _block_rehash() {
             // value if the module did not.
             $block['pages']  = '';
           }
+          /* The settings for custom, visibility, pages and title may have been altered for this block already,
+             in another theme. We need to retrieve these values so that the new row matches the exitsing block.
+             It should be acceptable to get these values from any existing row for this module/delta, because
+             all rows for this block will contain any customised values. However, for safety, and where the
+             block table has got mis-matched settings from before this addition was applied, we select the rows
+             ordered by bid, to ensure the earliest row is returned. If the block has not been customised then
+             this row will contain any values that were provided by the module, so again this is OK.
+             See http://drupal.org/node/115596 for details */
+          if ($existing_block = db_fetch_array(db_query("SELECT bid, theme, custom, visibility, pages, title FROM {blocks} WHERE module = '%s' AND delta = '%s' ORDER BY bid", $module, $delta))) {
+            $block['custom'] = $existing_block['custom'];
+            $block['visibility'] = $existing_block['visibility'];
+            $block['pages'] = $existing_block['pages'];
+            $block['title'] = $existing_block['title'];
+          }          
           // Add defaults and save it into the database.
           drupal_write_record('blocks', $block);
           // Set region to none if not enabled.