diff --git a/lib/filestorage/stored_file.php b/lib/filestorage/stored_file.php
index 3041a52a228..03653901501 100644
--- a/lib/filestorage/stored_file.php
+++ b/lib/filestorage/stored_file.php
@@ -142,8 +142,10 @@ class stored_file {
                     }
                 }
 
-                if ($field == 'referencefileid' or $field == 'referencelastsync' or $field == 'referencelifetime') {
-                    $value = clean_param($value, PARAM_INT);
+                if ($field === 'referencefileid' or $field === 'referencelastsync' or $field === 'referencelifetime') {
+                    if (!is_null($value) and !is_number($value)) {
+                        throw new file_exception('storedfileproblem', 'Invalid reference info');
+                    }
                 }
 
                 // adding the field
@@ -209,30 +211,33 @@ class stored_file {
             throw new coding_exception('An attempt to unlink a non-reference file.');
         }
 
-        // Remove repository info.
-        $this->repository = null;
-
         $transaction = $DB->start_delegated_transaction();
 
-        // Remove reference info from DB.
-        $DB->delete_records('files_reference', array('id'=>$this->file_record->referencefileid));
+        // Are we the only one referring to the original file? If so, delete the
+        // referenced file record. Note we do not use file_storage::search_references_count()
+        // here because we want to count draft files too and we are at a bit lower access level here.
+        $countlinks = $DB->count_records('files',
+            array('referencefileid' => $this->file_record->referencefileid));
+        if ($countlinks == 1) {
+            $DB->delete_records('files_reference', array('id' => $this->file_record->referencefileid));
+        }
 
-        // Must refresh $this->file_record form DB
-        $filerecord = $DB->get_record('files', array('id'=>$this->get_id()));
-        // Update DB
-        $filerecord->referencelastsync = null;
-        $filerecord->referencelifetime = null;
-        $filerecord->referencefileid = null;
-        $this->update($filerecord);
+        // Update the underlying record in the database.
+        $update = new stdClass();
+        $update->referencefileid = null;
+        $update->referencelastsync = null;
+        $update->referencelifetime = null;
+        $this->update($update);
 
         $transaction->allow_commit();
 
-        // unset object variable
-        unset($this->file_record->repositoryid);
-        unset($this->file_record->reference);
-        unset($this->file_record->referencelastsync);
-        unset($this->file_record->referencelifetime);
-        unset($this->file_record->referencefileid);
+        // Update our properties and the record in the memory.
+        $this->repository = null;
+        $this->file_record->repositoryid = null;
+        $this->file_record->reference = null;
+        $this->file_record->referencefileid = null;
+        $this->file_record->referencelastsync = null;
+        $this->file_record->referencelifetime = null;
     }
 
     /**