this seems to be a problem within the raw file, not lightroom.
Shoot both raw and jpeg. (Setting FINE+RAW)
Throw the jpegs away after the download.
Now the raw file gets interpreted correctly!
This has another advantage: On the camera you can zoom into the images to 100%, which you couldn't in raw only mode!!! After downloading from the SD you don't need the jpegs anymore if you are a raw shooter, so trash them.
Capture One 7, by the way opens it correctly either way. Still I think, the problem is not with adobe, but in the way the camera encodes the raw file (educated guess).
I use Photoshop (PS) no Lightroom, but I assume it is the same in LR since they both use ACR (adobe camera raw) as raw converter.
And now the interesting bit. If you investigate the metadata you find:
Raw Image Full Size : 5120x3288
This is 17,4 Megapixels instead of the
4896x3264 = 16Megapixel of the jpeg (and the raw in raw+FINE mode)
If you open the raw in Capture One and look at it, it has 4896x3264 (with or without the workaround).
But as you examine deeper you find a crop frame set to 4896x3264 which you can enlarge to 5120x3288 !!!!
This means you get the full 17,4MP!!! Meaning that there are additional margins on the image which you can use! I assume (but did not test it) that the viewfinder shows the 16MP crop. One more thing: 5120:3288 =1,55 So this is not the aspect ratio of 1,5 =3:2
Adobe ACR seems to be limited to the 16MP in any case.
What I did not find out is, where in the raw file the information about the crop frame is stored. In the exif I could not find it (but I might have overread it).
Capture One works straight forward + can give you 17,4MP
in any case:
turn on fine+raw
the cropframe of the raw will be set to the 4896x3264 (3:2) if you open in ACR.