The same items with different stacks will not combine each others stacks

I discovered this bug when I tried stack my oak logs from 51 and 13 to 64

 

One slot of oak logs has a stack value of 51

and the second slot of oak logs has stack value of 13

 

When I try to combine, it didn't work, like they think they are not the same item

 

They won't get stack with each other until you drop them on the ground and pick it up

 

Hope someone will notice this or add as a duplicate