Windows 8.1, latest java version.
I was about to continue working on my map so I loaded it in new snapshot. I was afraid that the new snapshot might break my map so I made a backup before I loaded it. When i started the world everything seemed just fine. But then i noticed that all my signs and custom heads on the world were missing. They didn't actually went missing, they were still there, I was able to step on them, clicked the signs and i was able to break them. Only their texture went missing. I tried all debug commands, but nothing worked. When i loaded it again in previus snapshot, their texture reapeared. So backup wasn't really needed.
How to recreate:
1. In creative inventory look for signs and heads.
2. Put them in your inventory.
3. Place them down.
4. Watch how they go invisble.
5. Fix the bug
I am also attaching 3 pictures, on the first picture i was in 17w06a snapshot and everything was normal. On the next two picture in was in 17w13a snapshot and you can't see their texture, but you can see their hitboxes.