Fences disappearing from hotbar

So here's the story: I was in multiplayer (LAN) survival mode, building a bridge with fences underneath. I craft the fences. They go into my inventory. I try placing them on the bottom of a block, and they show up for a blink of an eye, and disappear. Now, my internet is slow, so I figured it was just that. But after all 12 fences had just disappeared, I figured it was a bug with the snapshot.