A sign cannot and typed be placed on fences (unless under certain conditions

I expected to place a sign and type on it
that is what should have happened.

Instead the sign placed and didn't allow me to type
The sign placed and I could not type anything on it, but if I sneak + placed I was allowed to type.

Steps to make happen:
1. Place down a fence.
2. Place a Sign on the fence.
3. Place another fence
4. Place a sign (while sneaking) on the fence