short frame subband coding

I am implementing a subband ADPCM codec, Fs=16 kHz, frame length 3ms, band1=50Hz-2kHz, band2= 2kHz-8kHz. I used the FIR filter for subband coding and %50 overlap. My reconstructed signal does not follow the input. why it happens (it perhaps due to the short frame but I don't know what is happening) and how can I fix it?