Bug? Changing via agenda will lost undo info

Hi, as title, when I change a todo status via agentar by hitting ``t'', then go
back to the org file, I find that I can't undo anymore, emacs says:
    undo-more: No further undo information

emacs version:
    GNU Emacs 23.0.60.1 (i386-mingw-nt5.0.2195) of 2008-12-24 on mybox

orgmode version:
    Org-mode version 6.16

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Regards,
anhnmncb

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