When there is a block which breaks faster (block a) than a block which is behind the faster-breaking block (block b), block b will break faster if mined in succession with block a.

Example: under the circumstance in which the player is under the haste II affect, and block a is polished andesite and block b is cobblestone, cobblestone will break faster than its normal breaking speed when mined directly after the andesite.

Example 2: the same applies to snow layers and dirt-family blocks; due to the faster mining speed of snow, dirt breaks faster when mined in direct succession after a snow layer.