Sign Text stays after /setblock to another block

What I expected to happen was...
When I /setblocked a sign to stained clay, broke the clay, then placed a new sign, the new sign should be empty so I can type stuff on it.

What actually happened was...
When I /setblocked a sign to stained clay, broke the clay, then placed a new sign, the new sign had the same text the old sign had, including the colored json. When I clicked done, the colored text disappeared.

Steps to reproduce:
1. Place down a sign and type stuff on it.
2. /setblock another block at the sign's coordinates.
3. Break the new block and place an new sign. (no +NBT)