Plasing a sign on a sign can destroy the block

Placing a sign on an already placed sign can make that sign turn into the new one (not place the block but re-place it)

Steps to Reproduce:

1. get signs (With +DATA if posible but normal works too)
2. try to spam place the signs each time adjasoned to one another
3. try remembering the orientation

Observed Results:
the orientation of some signs has changed to the new ones (basicaly replaving them

Expected Results:
The sighs should still be stacking next to one another and not replacing them