I was trying to place a sign on top of a fence post. When I got done I noticed there were two signs, one with the text I entered and another one behind it with no text. So I broke the sign and tried again. This time only one sign appeared but there was no text. I tried again on the side of the fence post and the same thing happened. Attaching the sign to other kinds of blocks seemed to work properly.
Steps to reproduce:
1. Craft some signs and fence posts
2. place the fence posts
3. Attempt to attach signs to the fence posts
See attached screenshot: