please fix, i have to mine a block twice to brake it

What I expected to happen was
I only need to mine a block once to brake it = before =
What actually happened was
I had to mine a block twice to brake it = current =

Steps to Reproduce:
1. all you have to do is try and brake a block
all I actually know is this is what happens when oak wood with your hand in single player survival but I'm not Sure if that is the only place it happens and it happens no matter what (unless I'm on a server )