In 1:1 Navigator the preview is supposed to be pixel to pixel as I understand it.
This is easy on standard 72 dpi screens, but then we get Retina where the resolution can be changed. But no matter if the screen size of a 15" Retina screen is set to 1920 pixels wide or 1024 wide, the pixel of the 1:1 preview should till be 1:1.
This is how it is in Lightroom 3, but in the Lightroom 6 the 1:1 preview changes to approximately 1:2 when the same image is seen on the Retina screen (see bottom right screen dump).
What is this, and how can I change it so I get actual 1:1 preview (pixel to pixel preview) consistently with Lightroom 6 no matter which screen I use?
Below I have taken the screen dumps and put them together and you can see that the LR6 Retina preview changed to 1:2 when the LR6 window was moved to the Retina screen. It does so no matter what the screen resolution is set to, only the window showing the approx 1:2 preview changes in size as the screen inventory changes from 1920 pixels wide to 1024 pixels wide.
I have the same problem here on my 4K Dell Display (P2715Q) connected to my Retina MacBook Pro. The 1:1 Scaling is off, but only in the non-native resolutions. When I switch to the smallest native resolution of 3840x2160, the 1:1 seems to be correct. Very strange.