Display changes from Fullscreen to Widescreen automatically while watching a DVD

The automatic change from full screen to wide screen was caused by the DVD itself and the way the DVD was formatted.

In most cases, you should be able to access a menu on the DVD that lets you change the screen format to a format of your choice.  This can normally be found in the DVD's title menu, where you would also select play movie, special features, scene selection, and set up.

You may have to make this change for each DVD you play that is not widescreen.