I have seen similarly weird results with flaky USB flash keys. A lot of those don't do any kind of hardware error detection. The behavior described here can be

I have seen similarly weird results with flaky USB flash keys. A lot of those don't do any kind of hardware error detection. The behavior described here can be explained by block device cache: You write a file to a device and the device doesn't report an error, but doesn't actually write the data due to some hardware error. When you read the file back, the content will come from cache in your RAM, not the device itself. Unmounting and mounting the device flushes the cache. When you then read the file again, it will come from the device and have the original content again.