Submitting search form (mini) with enter key fires event handlers bound by jquery twice

app/code/Magento/Sales/Model/ResourceModel/EntityAbstract.php

@@ -121,10 +121,15 @@ protected function _beforeSave(\Magento\Framework\Model\AbstractModel $object)
     {
         /** @var \Magento\Sales\Model\AbstractModel $object */
         if ($object instanceof EntityInterface && $object->getIncrementId() == null) {
+            $store = $object->getStore();
+            $storeId = $store->getId();
+            if ($storeId === null) {
+                $storeId = $store->getGroup()->getDefaultStoreId();
+            }
             $object->setIncrementId(
                 $this->sequenceManager->getSequence(
                     $object->getEntityType(),
-                    $object->getStore()->getGroup()->getDefaultStoreId()
+                    $storeId
                 )->getNextValue()
             );
         }

app/code/Magento/Search/view/frontend/web/form-mini.js

@@ -207,6 +207,7 @@ define([
                     break;
                 case $.ui.keyCode.ENTER:
                     this.searchForm.trigger('submit');
+                    e.preventDefault();
                     break;
                 case $.ui.keyCode.DOWN:
                     if (this.responseList.indexList) {

app/code/Magento/Store/Model/PathConfig.php

@@ -76,6 +76,8 @@ public function shouldBeSecure($path)
      */
     public function getDefaultPath()
     {
-        return $this->scopeConfig->getValue('web/default/front', ScopeInterface::SCOPE_STORE);
+        $store = $this->storeManager->getStore();
+        $value = $this->scopeConfig->getValue('web/default/front', ScopeInterface::SCOPE_STORE, $store);
+        return $value;
     }
 }

app/design/frontend/Magento/luma/Magento_Checkout/web/css/source/module/checkout/_payments.less

@@ -58,6 +58,10 @@
                     }
                 }
             }
+
+            #po_number {
+                margin-bottom: 20px;
+            }
         }
 
         .payment-method-title {