Summary:
On Suspicious Sand cannot place almost all blocks that require support. You can only place signs and item frames. The expected results will be placing all blocks as on a full block (this is how Java works).

Steps to reproduce:

1. Place Suspicious Sand.
2. Try placing a block that requires a supporting block on Suspicious Sand (bell, redstone, lantern...).

Observed results:
Blocks are not placed on Suspicious Sand.

Expected results:
Blocks will be placed.