NOTE: This does NOT occur in 1.7.10 or lower, as I've attached a screenshot to show the difference between those versions.
What I expected to happen was for the glass panes to render as they did in 1.7.10 (screenshot attached).
What actually happened was that the texture became glitched out / mirrored, and maybe some z-fighting occurred as well.
Steps to Reproduce:
Just place down some glass panes in both versions and see the difference.