Here is an unusual story I experienced many months ago. First let me tell the reader what you are about to read is not normal. I have never heard of SELinux behaving like it did with me here, and I have used it for several years before and since this incident with no problems. (Though I have switched to using AppArmor based on recommendations from Ubuntu). I have also never had this problem since it happened.
Back on April 7th 2009, I installed Kubuntu Jaunty 9.04 KDE3 remix.
I did all the update and upgrades and grabbed all the new kernal goodness. Then I installed SELinux and rebooted. Upon reboot, I found something (SELinux I can only guess) had DESTROYED all the Japanese text in my filenames. It turned them into complete garbage and I don't know why, because this has never happened before. (I assume it did this during its scan of my hard-disks.)
In general I favor running SELinux and I don't believe this behavior is normal (especially since I have run it before and since with no more problems). I am thinking it was perhaps a problem with the package of SELinux itself from Ubuntu.
This type of file corruption would be a major catastrophe except that I am such a good person for backing files up, so I was able to recover from most of it.