Audio Video sync problems on HDTV and 6.1 surround

I'm running the Hitachi 42HDT52 hi-def plasma along with a Yamaha 6.1 suround receiver.

First off I'm running a pair of RCA patch cords from the stereo output of the dvd player (2 ch. stereo)to the plasma in the event I rather not turn on the Yamaha.

While viewing a movie on the plasma (dvd source) and listening to the audio on the yamaha (plasma speakers turned off)I noticed the video and audio are slightly out of sync.

While watching the movie and listening to the audio from the plasma speakers (2 ch. stereo) everything is fine.

While listening to the audio from both' the Yamaha and the plasma speakers' there's a slight time delay or echo effect.

Is this normal?