Output of KDF repeats

For the blocks of 64 bytes of output, the first and forth blocks are the same (among others). Since it is "H(0 XOR data)" and "H(0 XOR 1 XOR 2 XOR 3 XOR data)"

bscrypt.cpp

@@ -562,12 +562,13 @@ int bscrypt_kdf(void *output, size_t outputSize, const void *password, size_t pa
 
 	// Step 3: output = kdf(work, seed)
 	uint64_t i = 1;
+	uint64_t workSeed0 = workSeed[0];
 	while (outputSize > 64)
 	{
 		blake2b_nativeIn(output, 64, workSeed, 16 * sizeof(uint64_t));
 		output = ((uint8_t*) output) + 64;
 		outputSize -= 64;
-		workSeed[0] ^= i;
+		workSeed[0] = workSeed0 ^ i;
 		i++;
 	}
 	if (outputSize != 0)