DLP works by a grid of very tinny mirrors and a color wheel.
So let's say you have a 1080p TV. That grid will be a collection of mirrors that's 1920x1080.
Let's now talk about each mirror.
Each mirror makes up one pixel. When you apply electricity to the mirror, it becomes translucent. When you don't apply power, it bounces light. There is a color wheel that spins and for an equal amount of time shines 5 colors onto that mirror. If the mirror is electrified, that light just hits the bottom of your TV. If it's not, the beam is bounced to your screen. The way they can change the color of that pixel, is by how much light for each color to bounce to the screen.
So for example, if you wanted pure red, they would only turn on the mirror for the time the red section of the color wheel is passing in front of the light, and the rest of the time they would turn it off. If they wanted to mix colors, they would only keep it on for a short time between whatever colors they needed to mix that color. If you want pure black, you never allow the mirror to be reflective ,and if you want pure white, you always keep that mirror on.
Each mirror in that grid is doing this for each pixel on the screen. For those 20 pixels on your TV, the mirror is not responding to the single being sent to it to turn off.
That's what's going on. I don't know if there is a software reset to fix this, or if you will need repairs.