I'm using the Shuttle in combination with a mobile broadcast studio. The input in 720x576 pal, but the Shuttle records it in 4:3 while the input signal is 16:9. Does anyone know if it's possible to record in 16:9?

PAL 720/576 is always 4:3. So it records simply every pixel. It's only how you deliver the signal to your recorder (crop/letterbox/strech) and the way it is handled while replaying. I think in your case the monitor or NLE must process the image