[Discuss-gnuradio] DPSK mod/demod block work well?

[Songsong Gee]

I just made very simple dpsk mod/demod testing flow graph

you can see flow graph in following link: https://picasaweb.google.com/lh/photo/76z3sTbLs9Srz1N-wJhNzw?feat=directlink

When I run it, I found strange outcome from it: https://picasaweb.google.com/lh/photo/U0_S_71HzkL9t9RbeEBP2Q?feat=directlink

I didn't change any parameters in mod/demod blocks.

How can I get a good signal after mod/demodulation?