emacs slow down the system when switching from file mode to buffer mode in speedbar

[Qiang]

Emacs version: 
    GNU Emacs 23.0.60.1 (i686-pc-linux-gnu, GTK+ Version
    2.12.11) of 2008-12-13
System:
    Linux Qiang 2.6.26-gentoo-r4 #1 Mon Dec 22 20:50:07 CST 2008 i686
    Intel(R) Pentium(R) M processor 2.00GHz GenuineIntel GNU/Linux

After speedbar is activated, the current mode is "file mode". I pressed
"b", then it will switch to "Buffer mode". But it fails.

It will slow down the system. Very Slowly. Even I can not swith from
Emacs to other applications. 
Additionaly, i run "ps -ef". I find some kernel threads "[pdflush]" are
running.
Later, emacs will break.

Would you tell me how to solve it?

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