Using dqpsk and qbpsk modulations with benchmark_rv and benc

I was playing around with and using
different modulation schemes. When I run them with the gmsk modulation,
things work perfectly fine ( I am communicating between two usrps on two
different nodes). however, when I use dbpsk modulation, the machine
which runs the receive code hangs. So is it that there is a large amount
of computation done in the dbpsk demodulation, or is there a bug? Also
when I use the dqpsk modulation, stuff work but almost no packet is
received correctly. i.e. n_right is nearly 0 although most of the time
it can decode the packet seqno correctly. But, since dqpsk is
non-coherent I was expecting a much better performance. Kindly let me
know what the problem is.