I was coming in for a landing last night when I noticed that my Phantom 2 was coming down much faster than expected.  I let go of the stick to allow it to hover, but it kept coming down at full speed.  I pushed the stick up as hard as it would go, but it kept shooting down.  It then slammed into the ground (right side up), bounced, and landed upside down.  The propellers were still spinning very quickly, so I walked over and carefully turned the power off.  What would cause it to come down hard like that?

Other details:
Prior to this, my friend took it up too high (I told him not to touch the altitude, but next thing I knew he went from 150 ft to 1000+ feet) and activated Return To Home.  It landed softly without any problems.  I then restarted and recalibrated the phantom to reestablish control.  After the crash, I restarted and recalibrated the Phantom 2 to see if it was broken.  Oddly, the altitude reading was stuck at around 66 feet before take off, and it wouldn't allow me to set the ground altitude to the alt altitude.  I flew it up about 2 feet off the ground, and it everything seemed to work, except that the altitude was bouncing up and down by a bit (it typically hovers in place without any noticable movements).  The firmware has not been upgraded.  Aside from some scratches on top of the propellers where they were spinning into the ground after it bounced and flipped over, there doesn't appear to be any damage.

manual mod.  and why the heck would you have overriden the altitude setting so it could ven go to 1000 feet?  Not smart.

An advanced IMU calibration is highly recommended!