Signs invisible when placed under sand

I was building a wall of sand and wanted to make a door. So, 2 blocks up, I broke a block the immediately placed a sign (was trying things out), all the sand fell and broke like I placed a torch. But when it was done falling, the sign was invisible, it did not have any text on it. You could see the hotbox but not the texture. Attached is a screenshot of it.

Thanks,
Joshua

Edit: When I came back to take the screenshot, the texture was back,. I was able to reproduce it, but not take a screenshot, I am sorry. I could not get it to do it again, so I guess it is only every now and then.