I fainlly found the truth.
It is not a bug.
It is a feature of PB SS.
PB SS can't take whole screen by defaut settings.
pb_sv_ssWidth and pb_sv_ssHeight must be increased in order to
take whole image.
If you want to take whole screen of clients, you have to set these options
as high as client's resolution.
Add following 2commands to your PB config.so you can find it.
pb_sv_SsWidth 1024 //[Requested pixel width of remote screenshots]
pb_sv_SsHeight 768 //[Requested pixel height of remote screenshots]
THX ::SGM:: Original ZED
