problem when split window

[夏凯]

i use CTRL+a+S to split window in screen, but i can't input anything
in the region, and there is no more bash forked.
i can use CTRL+a+Tab to switch to the second region.
i can use CTRL+a+X to kill the second region, when i use CTRL+D to
exit the first region, i just exit the whole screen,
here is my snapshot:http://i.imgur.com/uX3CW.png
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