I've noticed the bounding box that shows you which block your cursor is pointing at is much darker now... but that isnt the bug. I like that change. The bug is that when you have your cursor pointing at a transparent block such as ice or stained glass while there is water behind them, the bounding box becomes hard to see. It becomes even harder to see with what I described above if it is dark and or night time.
I also found that something similar happens when you have your cursor pointing at transparent blocks that are up against the nether portal while is active.
It seems as if the water and portal animated textures are rendering ontop of the block selector's outline.
I have some pictures to show what I mean.

Also I did quite abit of searching and it looked like this bug hasnt been reported yet.