Convolutional code strange behavior

Hi everyone,

So whilst simulating a bursty channel I make use of the convolutional encoder. I obtain different BER values depending on if my binary input stream is a random stream or is the all zero codeword. Is this the normal expected behavior? What could be the reason for this? I suspect it might be due to the viterbi decoder. It should be noted that I use a decoding window of 5 times the constraint length. I can post the code if required but it is quite long.