comm.FSKDemodulator vs fskdemod function

Hi,

I'm trying to write a function that demodulates IQ data using BFSK. For this, I have access to a file that contains I and Q vectors. I tried both available ways to do this with communication Toolbox, namely using comm.FSKDemodulator and fskdemod function. However I obtained different results for the same set of data and with the same parameters for the demodulators, does anybody have an idea where the difference comes from?

Here is a example of my code

%I and Q vectors

IQ = complex(I,Q);
fs = 20e6;
bitrate = 2e6;
frequency_sep = 2*200e3

bit_stream = fskdemod(IQ,2,frequency_sep,fs/bitrate,fs);

demod_object = comm.FSKDemodulator('ModulationOrder',2,'FrequencySeparation',frequency_sep,...
    'SamplesPerSymbol',fs/bitrate,'BitOutput',true);
bit_stream2 = step(demod_object,IQ);

Thanks for you help