[Orgmode] time lag in re-scheduling the item in Agenda buffer

[Xin Shi]

Hi,

I'm using the 5.22a version.  When I view the agenda in the buffer, I 
use keyboard C-c C-s to re-schedule some items. It first gives a "nil" 
in the min-buffer, and after about 2 or 3 seconds gives me the calendar 
to choose. It looks like slow compared with doing the same thing in the 
.org file on those items. Are there any reason for that or to make it a 
little bit faster?

Thanks!

Xin