Apps on SD-Card

Hello,

I have my apps on SD card and a symlink in Qtopia/bin to my apps. 
The SD card is formated ext2.
It's works, but from time to time my apps on the card are set to a file
length of 0. 
What can be the cause? Not unmounted before power off?

This happens to me when I copy something to usb and plug out the usb flash
disk from my pc without unmount it.