Amaxingly i'd just opened up google to put the same search figures into !!!! - I acquired the image directly from the timeline of a 16:9 project within Premiere - File-Export Timeline - Frame
Shot on Sony PDX10 720x576 but using the 16:9 mode (this is true 16:9 capture, not just letterboxed - same as your XL2) - I'm going to grab a frame from something i've shot in 4:3 and will let you know the grabbed frame size
I've never ever grabbed frames as a rule but just needed one today. It's bizzare. I just went into premiere again and changed from D1/DV PAL (1.067) to Square Pixel setting, grabbed a frame and, hey presto the same 786x576 - Bizzare