Yesterday I preformed a display assembly replacement after my sister broke the front glass on her GSM iPhone 4. Everything went fine and after a short while, she had a working, new screen. Roughly 10 hours later, her phone is sitting stationary, she receives a text and the display is fine, then moments later receives another text and is instead greeted by what can best be described as a series of colored lines. For example, on reboot, instead of the silver apple logo, the phone displays a series of silver colored bars in running from top to bottom in the center of the screen where the logo should be. I'm linking to a photo that should hopefully illustrate it better than I can. I've opened the phone back up and re-seated and cleaned the connections between the logic board and display several times to no avail. So what I'm asking is: Is the display assembly defective or was it an error in installation?

Image of phone's display post-repair.