I placed a gravel block against a wall on a water source block and then the gravel fell and there was an air block. (Im assuming this might also happen with sand and concrete)
MC-131065
Gravel makes an air pocket when placed against a wall and falls down in water
Resolved
Works As Intended
0
You're replacing the water with a gravel block. The gravel then realizes it shouldn't be there and will fall. All intended.