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:
Place Suspicious Sand.
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.
They also the bamboo isn't planted on suspicious gravel