OK, I have good news and I have bad news.
I have been able to recreate the problem on my system.
The good news is that it is nothing to worry about for most people. If you add effects and you have to render to get real time playback, it does squish the images leaving a black border. However, it doesn't export that way as far as I can tell, even if you tell it to use the render files, which I never, ever do, for any of my videos. If you create titles or masks that require exact dimensions, it appears that you can use the squished image and it will expand as required upon export. That requires further testing by someone who needs to edit this way. I don't.
If you delete the render files, the images go back to normal. So you could generate your masks and titles that way and then just render again.
The bad news is that it does appear to be a bug that needs to be fixed because it will certainly confuse any clients looking over your shoulder. If you render the entire work area, thinking that since you didn't add any effects to most of it there should not be a problem, think again. You don't need to add effects for the problem to appear.
So, it is off to put in a bug report. https://www.adobe.com/cfusion/mmform/index.cfm?name=wishform
However, something tells me that if this is not an easy fix, it might end up on the bottom of the pile of reports. I doubt that there are many people editing video using the DSLR images at full size. Why? How would anyone play them back? The biggest screen I have is 1920X1080 and I am pretty much ahead of the curve. Most people who do not edit video have screens with smaller dimensions.
Eventually that will change as people get 4K televisions, so it might be a really good idea to fix it now rather than wait until the last minute and fail to get it into the release that hits just before the Christmas sales of 4K televisions at Sears and Walmart.
For those of you playing along at home it looks like the second image below. Look at the righthand edge:
Image may be NSFW.
Clik here to view.
Image may be NSFW.
Clik here to view.
