Aspect Ratio Changes Randomly?

I recently got a Toshiba 32Z44 and over the past few weeks I have noticed that sometimes when watching a 4:3 TV program or playing a 4:3 DVD / Game that the picture will randomly stretch to fill the whole screen and then afew second later go back to normal.

Has anyone else had or heard of a problem like this before?

 

My Tosh (ZT29) also does it occasionally. Don't know why though. Always the same places on the same DVDs, so I assumed it saw a dark edge and assumed it should switch ratio.

 

Have just tested a DVD which gave the problem afew days ago and it does change the picture ratio at the same spot everytime so I guess its not so random after all.