if he only lost about 5mb after removing apps, then it means that his rootfs is screwed/full of ****. i had the same problem when installing nitdroid.
i dont think cssu is to blame, but to fix this:
1. reflash your phone to pr1.3
2. DONT INSTALL ANY APPS
3. install cssu only
4. test it to see if stable or not
5a. if stable proceed to install apps
5b. if unstable reflash to pr 1.3 and just use that