It's written asap to disk unless you configure it otherwise. The disk (or flash disk, in your case) has its own ram before actually flushing to physical storage

It's written asap to disk unless you configure it otherwise. The disk (or flash disk, in your case) has its own ram before actually flushing to physical storage (fsync, unless it lies, in which case there is probably an article about it here cough macs cough). So the kernel isn't lying to you, but your disk probably is.