The developers have replied that the serial pin will be in an undefined state before it is initialized. So I have put a work around in software: I just ignore all characters before a known marker is received. This works well for me, for now. But this is only sweeping the problem under the carpet.

Probability theory says that if sufficient number of monkeys type randomly for sufficient number of years, then you can expect to see a quote from Shakespeare in their output!

If an uninitialized output pin is going to be in an undefined state, by design, it is a ticking time bomb. Such engineering practices have resulted in exploding space shuttles and melting nuclear reactors!

A better design would be to start the pins in INPUT mode by default. Software can take several milliseconds to complete its boot up routines, read configuration settings etc., before initializing the serial port. Till then the port can at least be silent.