This appears to be a bug in ACR7.2 and Lightroom 4.2RC:
When importing RAW shots made with a Sony RX100, in the RAW+JPEG mode, when the JPEG part was set to less than 20Mpixel, Lightroom 4.2RC will misidentify the files as being cropped and will show a crop box centered on the image, even though both the raw and the JPEG did use the full size image. This happens regardless of the used aspect ration, i.e. the crop is not because of the use of a non-native aspect ratio.
Other reports of the same issue:
http://forums.adobe.com/message/47039...
http://forums.adobe.com/thread/1067177
http://forums.adobe.com/message/46788...