.paymentInfo never mutates the existing signature (#5659)

packages/api/src/submittable/createClass.ts

@@ -160,9 +160,11 @@ export function createClass <ApiType extends ApiTypes> ({ api, apiType, blockHas
               // setup our options (same way as in signAndSend)
               const eraOptions = makeEraOptions(api, this.registry, allOptions, signingInfo);
               const signOptions = makeSignOptions(api, eraOptions, {});
-              const u8a = this.isSigned
-                ? api.tx(this).signFake(address, signOptions).toU8a()
-                : this.signFake(address, signOptions).toU8a();
+
+              // 1. Don't use the internal objects inside the new tx (hence toU8a)
+              // 2. Don't override the data from existing signed extrinsics
+              // 3. Ensure that this object stays intact, with no new sign after operation
+              const u8a = api.tx(this.toU8a()).signFake(address, signOptions).toU8a();
 
               return api.call.transactionPaymentApi.queryInfo(u8a, u8a.length);
             })

packages/types/src/extrinsic/v4/Extrinsic.ts

@@ -35,8 +35,8 @@ export class GenericExtrinsicV4 extends Struct implements IExtrinsicImpl {
   public static decodeExtrinsic (registry: Registry, value?: Call | Uint8Array | ExtrinsicValueV4, isSigned = false): ExtrinsicValueV4 {
     if (value instanceof GenericExtrinsicV4) {
       return value;
-    } else if (value instanceof registry.createClassUnsafe('Call')) {
-      return { method: value as Call };
+    } else if (value instanceof registry.createClassUnsafe<Call>('Call')) {
+      return { method: value };
     } else if (isU8a(value)) {
       // here we decode manually since we need to pull through the version information
       const signature = registry.createTypeUnsafe<ExtrinsicSignatureV4>('ExtrinsicSignatureV4', [value, { isSigned }]);