There’s a new wrinkle in the ABC vs. CBS, Dave vs. Ted, Dave vs. Jay situation on the late-night TV front. “Good Morning America” host and ABC news fixture Diane Sawyer, 56, has abruptly backed out of a scheduled guest appearance on CBS’s “Late Show” with David Letterman, reports New York’s Daily News. “Diane enjoys doing the Letterman show,” ABC News spokesman Jeffrey Schneider, told the paper, “but she’s decided to postpone it.” The booking was reportedly made two months ago, long before the news broke that ABC is attempting to woo Letterman, 57, away from CBS by promising him the slot currently occupied by the 22-year-old news program “Nightline,” hosted by Ted Koppel. The announcement, which came as a surprise even to the head of ABC News, has provoked a groundswell of support for Koppel, especially in the TV journalistic community. Sawyer has yet to comment publicly on the Koppel-Letterman matter. She was due to appear on the “Late Show” on Tuesday to promote her upcoming interview with talk-show host Rosie O’Donnell. “Diane has always been a fantastic guest, Letterman’s executive producer Rob Burnett told the News through a spokesperson, “and she’s welcome back on the ‘Late Show’ anytime.” The talk-show host himself is away this week, said to be vacationing in St. Bart’s. Negotiations between his camp and CBS and ABC continue.