config_default_inc.php:
/**

• access level needed to re-open bugs
• @global int $g_reopen_bug_threshold
  */
  $g_reopen_bug_threshold = DEVELOPER; // (I set it to the REPORTER, so that's why this question appears)

So this option allows bug reopening for the specified access level (all bugs, independently of $g_allow_reporter_reopen).

But when we try to reopen smb. else's bug we see 'reopen' button, press it, and get 'Access denied' reply.

It happens because of bug_update.php, line 73:
It checks 'update_bug_threshold' or then $g_allow_reporter_reopen-related access but not $g_reopen_bug_threshold.

if ( !(
( access_has_bug_level( access_get_status_threshold( $f_new_status, bug_get_field( $f_bug_id, 'project_id' ) ), $f_bug_id ) ) ||
( access_has_bug_level( config_get( 'update_bug_threshold' ) , $f_bug_id ) ) ||
( ( bug_get_field( $f_bug_id, 'reporter_id' ) == auth_get_current_user_id() ) &&
( ( ON == config_get( 'allow_reporter_reopen' ) ) ||
( ON == config_get( 'allow_reporter_close' ) ) ) )
) ) {
//echo ("Access denied!"); die();
access_denied();
}

I suppose there must be an additional check for the $g_reopen_bug_threshold:

if ( !(
( access_has_bug_level( access_get_status_threshold( $f_new_status, bug_get_field( $f_bug_id, 'project_id' ) ), $f_bug_id ) ) ||
// Watergad: reopen threshold check
( access_has_bug_level( config_get( 'reopen_bug_threshold' ) , $f_bug_id ) ) ||
( access_has_bug_level( config_get( 'update_bug_threshold' ) , $f_bug_id ) ) ||
( ( bug_get_field( $f_bug_id, 'reporter_id' ) == auth_get_current_user_id() ) &&
( ( ON == config_get( 'allow_reporter_reopen' ) ) ||
( ON == config_get( 'allow_reporter_close' ) ) ) )
) ) {
//echo ("Access denied!"); die();
access_denied();
}

Add this to the future releases please if it's really bug and not my misunderstanding of the $g_reopen_bug_threshold principles.