Who needs dvd's, anyway?

For the first time in years(!) I have to deliver a video on dvd. Yes, I have burned the occasional dvd but almost all of my work is delivered as webfilm, in quicktime. This client wants 25 dvd's, too small a number to go to the shop so I burn it myself. Real old-fashioned handmade dvd's.
I burn 25 of them and test a few on my standalone dvd-player (which has become obsolete since I got my WD Mediaplayer 2 years ago). I also play them on my Mac and Windows PC. All is well.
I give the dvd's to my client, who gave it to hér boss to view it at home. He returns the dvd saying it doesn't play well: the lower thirds with his name & title are cut off horizontally. I ask for the dvd so I can check if it's bad. I insert it into my dvd-player and it plays fine, as expected. Then I decide to try to recreate the problem and all becomes clear when I set the dvd-player to display 4:3. It cuts off the picture exactly where he told us.