Aspect ratio problem using DVD+R but not DVD-R

This is a strange one. I converted and burned some native 4:3 videos to DVD, but on TV the video was stretched somewhere between 4:3 and 16:9 (just displaying the native 3:2 maybe?). Much trial and error ensued, and it turns out that the exact same DVD burned to a DVD-R disc displayed fine, but using a DVD+R futzed the A/R. Using my PS3 as a player, I also saw that with the DVD+R, the TV resolution switches down to 720 * 480, while with the DVD-R, it stays at 1280 * 720.

So, two questions: 1) Howcum? and 2) How do I make burning DVDs to DVD+R work? (I'm using Imgburn, if that makes a difference.)