Can't edit sign that are put on fences

I tried to put a sign on a fence but it just places a sign and doesn't let me edit-it.

What I though would happen:
Put the sign on fence then edit it.

What really happend:
Put the sign on the fence just places the sign and doesn't let me edit-it.

Steps to Reproduce:
1.log into minecraft
2.start game
3.go on a server(creative)
4.try to put a sign on a fence