In LR CC 2015.3, in Library Mode / Second Screen / Loupe View / 1:3 Zoom, LR shows me by default the view on the left in the image below  ie the one that's slightly blurred.
However, for no apparent reason, the view is sharpened when I press left-mouse button (and hold it down). When I release the left-mouse button, the image reverts to being blurry.
This is a painful part of the LR experience and I'd say it's a bug because I have to ask myself, "which of these two is the correct representation of the image?". When you have to ask that question, the editing environment is broken and the editing experience is more painful.
My questions are:
1) Is this a bug or a feature?
2) How do I know which is the most accurate representation of my image?
3) Either way, why not simply show the most accurate representation of my image ie why make me try and guess?