diff --git a/src/jrd/extds/InternalDS.cpp b/src/jrd/extds/InternalDS.cpp
index 7d9d582cd1..2aeba54223 100644
--- a/src/jrd/extds/InternalDS.cpp
+++ b/src/jrd/extds/InternalDS.cpp
@@ -209,7 +209,7 @@ void InternalConnection::doDetach(thread_db* tdbb)
 		FbLocalStatus status;
 
 		RefPtr<JAttachment> att = m_attachment;
-		m_attachment = NULL;
+		m_attachment = NULL;	// release and nullify
 
 		{	// scope
 			EngineCallbackGuard guard(tdbb, *this, FB_FUNCTION);
@@ -369,7 +369,7 @@ void InternalTransaction::doCommit(FbStatusVector* status, thread_db* tdbb, bool
 	if (m_scope == traCommon && m_IntConnection.isCurrent())
 	{
 		if (!retain) {
-			m_transaction = NULL;
+			m_transaction = NULL;	// release and nullify
 		}
 	}
 	else
@@ -380,7 +380,10 @@ void InternalTransaction::doCommit(FbStatusVector* status, thread_db* tdbb, bool
 		if (retain)
 			m_transaction->commitRetaining(&s);
 		else
+		{
 			m_transaction->commit(&s);
+			m_transaction.clear();
+		}
 	}
 }
 
@@ -390,14 +393,14 @@ void InternalTransaction::doRollback(FbStatusVector* status, thread_db* tdbb, bo
 
 	if (m_connection.isBroken())
 	{
-		m_transaction = NULL;
+		m_transaction.clear();
 		return;
 	}
 
 	if (m_scope == traCommon && m_IntConnection.isCurrent())
 	{
 		if (!retain) {
-			m_transaction = NULL;
+			m_transaction = NULL;	// release and nullify
 		}
 	}
 	else
@@ -408,12 +411,15 @@ void InternalTransaction::doRollback(FbStatusVector* status, thread_db* tdbb, bo
 		if (retain)
 			m_transaction->rollbackRetaining(&s);
 		else
+		{
 			m_transaction->rollback(&s);
+			m_transaction.clear();
+		}
 	}
 
 	if ((status->getErrors()[1] == isc_att_shutdown || status->getErrors()[1] == isc_shutdown) && !retain)
 	{
-		m_transaction = NULL;
+		m_transaction.clear();
 		status->init();
 	}
 }
@@ -618,7 +624,7 @@ void InternalStatement::doOpen(thread_db* tdbb)
 		if (m_cursor)
 		{
 			m_cursor->close(&status);
-			m_cursor = NULL;
+			m_cursor.clear();
 		}
 
 		fb_assert(m_inMetadata->getMessageLength() == m_in_buffer.getCount());
@@ -661,9 +667,11 @@ void InternalStatement::doClose(thread_db* tdbb, bool drop)
 		EngineCallbackGuard guard(tdbb, *this, FB_FUNCTION);
 
 		if (m_cursor)
+		{
 			m_cursor->close(&status);
+			m_cursor.clear();
+		}
 
-		m_cursor = NULL;
 		if (status->getState() & IStatus::STATE_ERRORS)
 		{
 			raise(&status, tdbb, "JResultSet::close");
@@ -672,10 +680,12 @@ void InternalStatement::doClose(thread_db* tdbb, bool drop)
 		if (drop)
 		{
 			if (m_request)
+			{
 				m_request->free(&status);
+				m_request.clear();
+			}
 
 			m_allocated = false;
-			m_request = NULL;
 
 			if (status->getState() & IStatus::STATE_ERRORS)
 			{
@@ -835,7 +845,7 @@ void InternalBlob::close(thread_db* tdbb)
 	{
 		EngineCallbackGuard guard(tdbb, m_connection, FB_FUNCTION);
 		m_blob->close(&status);
-		m_blob = NULL;
+		m_blob.clear();
 	}
 
 	if (status->getState() & IStatus::STATE_ERRORS)
@@ -855,7 +865,7 @@ void InternalBlob::cancel(thread_db* tdbb)
 	{
 		EngineCallbackGuard guard(tdbb, m_connection, FB_FUNCTION);
 		m_blob->cancel(&status);
-		m_blob = NULL;
+		m_blob.clear();
 	}
 
 	if (status->getState() & IStatus::STATE_ERRORS)