Some slabs' hardness values do not match their base blocks' values

Some slabs break slower than their base blocks. These blocks are:

• Sandstone

• Cut Sandstone

• Red Sandstone

• Cut Red Sandstone

• Quartz Block

How to reproduce:

1. Obtain the aforementioned blocks in large quantities and make some of them into slabs.

2. Place them down.

3. Try to break them with a wooden pickaxe.

4. Find out that slabs break slower.