Placing a sign on the same block as another block deletes the other block

Original Summary
Placing a sign on the same block as an end rod deletes the end rod

Summary:
When a sign is placed in a block space where another block already exists, the other block is deleted.

Steps to Reproduce:

1. Place a block.
2. Place a sign in the same space as the block placed in step 1 (by pointing at an adjacent block that you can attach the sign to).

Observed Results:
The block placed in step 1 is deleted.

Expected Results:
The sign should not be placed.