Problems persisting Core Data structures on iPhone/iPad

I have an iPhone/iPad app using Core Data to keep my application data. Sometimes, even though I don't get any error messages, the data is not really save开发者_开发技巧d so when the app starts anew, it's all gone. This problem seems to disappear after physically rebooting the device, but otherwise it's pretty random and hard to track. Has anyone seen a similar issue?

Also, it seems to happen more often in the iPhone 1st generation, less so in the 3G/3GS, and seldom in the iPad. Very strange...