DPSK block problem

I want to send an receive data with DPSK modulation
So I made a simple testing GRC graph
https://picasaweb.google.com/lh/photo/wYSKGiQz-0xB5EXtfEe_HQ?feat=directlink

Originally, I separated TX part and RX part, TX part performs DBPSK mod
and
passes to USRP sink
and RX part USRP source gives a signal and performs DBPSK demod and plot
it

Currently I put them together into one grc graph, but the result are all
same
So you just can understand it’s no problem

The real problem is the received signal is not what I expected.
Here is the received signal waveform.
https://picasaweb.google.com/lh/photo/63zs3JdmyAS-oMCyyh17Ug?feat=directlink
The bottom is the modulated signal, and the upper is the demodulated
signal

BUT what I expected after demodulation is like below:
https://picasaweb.google.com/lh/photo/H9RItzjpfemHy-OR2eQhQg?feat=directlink
And this is same as the original source.
(Except the magnitude, after demodulation I want rectangular pulse with
magnitude 1)

Might be, It seems I don’t understand parameters of DPSK (de)mod blocks
I