diff --git a/commands/core/cache.drush.inc b/commands/core/cache.drush.inc
index b48d1734c9..0bc10a1d6a 100644
--- a/commands/core/cache.drush.inc
+++ b/commands/core/cache.drush.inc
@@ -23,6 +23,7 @@ function cache_drush_command() {
     'outputformat' => array(
       'default' => 'print-r',
       'pipe-format' => 'var_export',
+      'output-data-type' => TRUE,
     ),
     'aliases' => array('cg'),
   );
diff --git a/commands/core/config.drush.inc b/commands/core/config.drush.inc
index 7876d492ab..d53f09b5cb 100644
--- a/commands/core/config.drush.inc
+++ b/commands/core/config.drush.inc
@@ -46,6 +46,7 @@ function config_drush_command() {
     'outputformat' => array(
       'default' => 'yaml',
       'pipe-format' => 'var_export',
+      'output-data-type' => TRUE,
     ),
     'aliases' => array('cget'),
     'core' => array('8+'),
diff --git a/commands/core/outputformat.drush.inc b/commands/core/outputformat.drush.inc
index 1d4f97b8a0..8b0f5c910a 100644
--- a/commands/core/outputformat.drush.inc
+++ b/commands/core/outputformat.drush.inc
@@ -275,7 +275,7 @@ function outputformat_drush_help_alter(&$command) {
       // If the command does not define specific field labels,
       // then hide the help for --fields unless the command
       // works with output format engines that format tables.
-      if (isset($outputformat['require-engine-capability'])) {
+      if (isset($outputformat['require-engine-capability']) && is_array($outputformat['require-engine-capability'])) {
         if (!in_array('format-table', $outputformat['require-engine-capability'])) {
           unset($command['options']['fields']);
         }
@@ -355,10 +355,10 @@ class drush_outputformat {
     return ($this->formatter_type() == 'list') && ($this->sub_engine->supports_single_only());
   }
   function data_type($metadata) {
-    if (isset($metadata['metameta']['require-engine-capability'])) {
+    if (isset($metadata['metameta']['require-engine-capability']) && is_array($metadata['metameta']['require-engine-capability'])) {
       return  $metadata['metameta']['require-engine-capability'][0];
     }
-    if (isset($metadata['require-engine-capability'])) {
+    if (isset($metadata['require-engine-capability']) && is_array($metadata['require-engine-capability'])) {
       return  $metadata['require-engine-capability'][0];
     }
     return 'unspecified';
diff --git a/includes/engines.inc b/includes/engines.inc
index 9b4e8990bf..27e6c0ca46 100644
--- a/includes/engines.inc
+++ b/includes/engines.inc
@@ -162,8 +162,8 @@ function drush_merge_engine_data(&$command) {
           unset($config[$engine_option_alias_name]);
         }
       }
-      // Make sure that 'require-engine-capability' is always an array.
-      if (isset($config['require-engine-capability']) && !is_array($config['require-engine-capability'])) {
+      // Convert single string values of 'require-engine-capability' to an array.
+      if (isset($config['require-engine-capability']) && is_string($config['require-engine-capability'])) {
         $config['require-engine-capability'] = array($config['require-engine-capability']);
       }
       $command['engines'][$engine_type] = $config;
@@ -239,10 +239,15 @@ function drush_merge_engine_data(&$command) {
           // it is assumed that the engine can satisfy all requirements.
           if (array_key_exists('engine-capabilities', $data)) {
             $engine_is_usable = FALSE;
-            foreach ($config['require-engine-capability'] as $required) {
-              // We need an engine that provides any one of the requirements.
-              if (in_array($required, $data['engine-capabilities'])) {
-                $engine_is_usable = TRUE;
+            // If 'require-engine-capability' is TRUE instead of an array,
+            // then only engines that are universal (do not declare any
+            // particular capabilities) are usable.
+            if (is_array($config['require-engine-capability'])) {
+              foreach ($config['require-engine-capability'] as $required) {
+                // We need an engine that provides any one of the requirements.
+                if (in_array($required, $data['engine-capabilities'])) {
+                  $engine_is_usable = TRUE;
+                }
               }
             }
           }
@@ -254,7 +259,7 @@ function drush_merge_engine_data(&$command) {
             $engine_data['options'][$option]['description'] = array_key_exists('description', $data) ? $data['description'] : NULL;
             if ($combine_help) {
               $engine_data['options'][$option]['hidden'] = TRUE;
-              if (drush_get_context('DRUSH_VERBOSE') || !isset($data['verbose-only'])) {
+              if (drush_get_context('DRUSH_VERBOSE') || ($default == $engine) || !isset($data['verbose-only'])) {
                 $combine_help_data[$engine] = $engine . ': ' . $data['description'];
               }
             }