Restore Point missing after disk wiping


After a 7-pass US DoD 5220-22.M disk wipe (cluster tips too) on Windows XP SP-1 the System Restore Point I made before using Eraser was missing. My hard drive is not compressed. I still think Eraser is one of the best disk wipers there is. I also use iolo's System Shield Professional.
I think Windows deletes restore points when it runs low on disk space, which is exactly what happens when Eraser is overwriting the free disk space.