Standalone mode uses temp DB files by default (RIPD-1129):

* If a [database_path] is configured, it will always be used, and tables
  will be upgraded on startup.

src/ripple/rpc/impl/TransactionSign.cpp

@@ -280,7 +280,7 @@ checkTxJsonFields (
     }
 
     // Check for current ledger.
-    if (verify && !config.RUN_STANDALONE &&
+    if (verify && !config.standalone() &&
         (validatedLedgerAge > Tuning::maxValidatedLedgerAge))
     {
         ret.first = rpcError (rpcNO_CURRENT);