just stitched a new Gigapixel (15 Gigapixels) with the latest 2.5 Beta - and the image looks a bit weird. Like if there is massive vignetting - but at our older shoots such problems never arrised - using the same lens and camera. (and I guess vignetting can't arise just the other day?!?)
guess you are right with "lens wide open aperture vigneting" - this gpix was shot by a colleague and he forgot to stop down the lens :-( Removed the vigneting with Lightroom + lens profile - but Autopano won't stitch em again - always crashes with this error message:
(critical error, happens at stage "color matching", 3. try now)
This error can arise when having a wrongly optimized panorama and doing color correction on that. So process in step : uncheck color correction, do detection, see if everything is okay ( geometrically ). Then enable color correction.
My guess in this case is that you lost exif in input file, then you go a bad panorama.