Hi!
I just found a bug in the current verison of Minecraft (1.8.7)
The problem being simple, yet hopefully it can be fixed!

So here's the issue. Holding a barrier block doesn't show other ones. They act as if you're not holding one in your hand (they're invisible even though I'm holding one. I know that there's a delay from when you pull one up until they start showing. But they dont show at all :s) It's not a huge problem. But worth mentioning!

Have a great day!
/Alfred