Ever since version 4.3 of Lightroom (I think it was 4.3 anyway) there has been this minor, but really annoying bug with the way images are displayed in the develop module. Basically, every time you move from one photo to another the image loads at full quality for a second, then drops to a low res blurry version for a couple of seconds before becoming clear again. If you have a small screen it's probably not that noticeable but on my 27" display it's really annoying. I've made a little video to show you what I'm talking about (You'll need to view it large to see the problem)
I know it's not really that big a deal, and it doesn't stop you working, but it does slow things down, and I find it really annoying. If anyone knows of any solutions to this 'd love to hear it. I have previews generated at 1:1 and they are of full quality.