Signs placed on string break when walking into it

When you place a sign on string and then you walk in the same block as the sign or string it pops off the sign. This is annoying if you're building some thing nice but functional because then you can't use the signs.

Steps to Reproduce:

1. Place string.
2. Place a sign on the string.
3. Walk into the string/sign.

Observed Results:
The sign breaks.

Expected Results:
The sign should stay placed on the string.