Toshiba 36ZP38B Dolby 5.1

Hello to all , I was wondering if anyone had experience of a particular sound problem which I have when watching Dolby 5.1 DVD's on my Toshiba 36ZP38B.

I have a dvd player connected via the Optical output to the Optical input on the telly. The telly plays Dolby 5.1 fine, but, I have noticed that when the dvd changes sound from ordinary stereo to 5.1 (normally at the main menu where you select the film to start) there is a very short cut in sound as the sound changes to 5.1. It seems to happen because the telly has reconised a change in signal and therefore is changing its output accordingly.

I have never had a Dolby 5.1 setup before and was just wondering if this is common?