The fix for PHPBB3-7972 (https://github.com/phpbb/phpbb3/commit/b73d45ffc8f35ae2112d5c4bb80dcdac0d5ce6ae) isn't quite correct.

When using the Copy topic feature of the MCP, the following error is thrown:

[phpBB Debug] PHP Notice: in file /includes/mcp/mcp_main.php on line 1051: Undefined index: enable_indexing

The first code block that was added which checks to see if indexing is enabled needs to be moved into the foreach at line 1082, since $topic_data is multidimensional. $topic_data['enable_indexing'] would then need to be changed to $topic_row['enable_indexing']. Now that indexing is checked, another error comes up:

[phpBB Debug] PHP Notice: in file /includes/mcp/mcp_main.php on line 1193: Undefined index: post_id

In the second block that was added, on line 1192, $sql_ary['post_id'] should be $new_post_id.