My 3GS crashed, I restored it to 3.1.3, and now say if I sync back an app that I used to have or download an app that I used to have ( before the crash), it will install, and then completely disappears from the iPhone home screen (same thing happens if I install it with iTunes, it installs but doesn't appear on the iPhone home screen). Spotlight search doesn't pick it up either. But I can still download other apps just fine, just not ones that my account downloaded before (they download and install but just disappear). What should I do to get them back?