Open-File Dialog and Save-As File Dialog is extremely slow on KDE

[H Xu <xusubsc@gmail.com>]

Hello,

I'm using Debian Wheezy, with KDE as the default installed Desktop 
Environment. However, every time a Open-File Dialog or Save-as Dialog 
pop up, the GUI becomes extremely slow: It takes seconds to drag down 
the scroll bar of the Dialog, takes seconds to enter a new directory. 
Could anyone tell me what is wrong with this?

Thanks,
Hong