BUG? Crypto++ 5.2.1 cfb_mode decryption (instance works, external doesn't)

[Altec]

Decrypting using external block cipher produces bad results while 
decrypting using instance works fine.

NOTE: The same scenarios work fine with encryption--only decryption 
produces different results between external vs instance (with external 
producing bad results during decryption).

Snippet:
//pEnc contains encrypted data.
size = 16;
if(1){
        //this produces expected/good pDec values
        CFB_Mode<AES >::Decryption m_SymmetricDec(keyDigest, 16, iv);     
        m_SymmetricDec.ProcessData((byte*)pDec, pEnc, size);
} else {
        //this produces bad pDec values
        m_pBlockCipherDec = new CryptoPP::AES::Decryption(keyDigest,16);
	m_pSymmetricDec = new 
CFB_Mode_ExternalCipher::Decryption(*m_pBlockCipherDec, iv);

        m_pSymmetricDec->ProcessData((byte*)pDec, pEnc, size);               
}