The Bug
The Mud Brick Slab has a much slower mining speed then the other Mud Brick Blocks
Reproduce
Get a Mud Brick Slab
Place it and mine it with your hand
Notice how long it takes
Place down any other Mud Brick block
Mine it with your hand
Notice how long it takes
Observed Result
The Mud Brick Slab took longer to mine
Expected Result
The Mud Brick Slab would take about the same time as the other mud brick related blocks
I can confirm this behavior. This is likely due to the fact that mud brick slabs copy the block properties of stone. Relates to MC-249313.