PumpMessages in crypto++, reading a key file?

I'm writing an AES key and iv to the file with crypto++ by using following code:

// write the key:
SecByteBlock key(AES::DEFAULT_KEYLENGTH);
SecByteBlock iv(AES::BLOCKSIZE);

string file = m_file_name + ".key";
FileSink* key_out = new FileSink(file.c_str());
Base64Encoder base64_key_enc(key_out);

base64_key_enc.Put(key.BytePtr(), key.size());
base64_key_enc.MessageEnd();
base64_key_enc.Put(iv.BytePtr(), iv.size());
base64_key_enc.MessageEnd();

and to read a the key and iv from the file back I use following:

// read key
string file = m_file_name + ".key";
SecByteBlock key(AES::DEFAULT_KEYLENGTH);
ArraySink* arr_key_in = new ArraySink(key, key.size());
Base64Decoder* base64_key_dec = new Base64Decoder(arr_key_in);
FileSource source(file.c_str(), false, base64_key_dec);
source.PumpMessages(1); // read only the key 

// read iv
SecByteBlock iv(AES::BLOCKSIZE);
ArraySink* arr_iv_in = new ArraySink(iv, iv.size());
base64_key_dec->Detach(arr_iv_in);
source.PumpAll(); // read the rest (the iv)

Problem is that after reading a file the key is correct but iv is not, so i wornder what could be wrong with my sintax?

the contents of a key file are base64 hex encoded and it looks like so:

2Gnh3TbAJeQPmza9FKdqNg== FowuKut3pBl7g0Or+4FJUg==

the == means end of the message/key... First on is the key, while the other one is the iv, the above code does not read the iv from the file properly.

What is wrong with my code?