Prior to 1.0, serial output was blocking. With 1.0, serial output is buffered, and output as time permits.
You are going to sleep before the output has completed. If you had code to wake up regularly, you should see serial data resume when you woke up.
The Serial.flush() function now blocks until the last character has shifted into the output register (not until it has been sent). You might need to use that (and a microscopic delay to get that last byte out) to get all the data out before napping.