DO NOT SAY THIS ISSUE IS INVALID. This issue has existed since stair blocks were added to the game (Alpha 1.0.0), so I think it's waited more than long enough.

A stair block is, in essence, three quarters of a full block, meaning that, as full blocks contain four quarters, the six full blocks which are used to craft any type of stairs should produce eight stair blocks rather than four (6 x 4 = 24, 24 ÷ 3 = 8). This has always annoyed me - and I think it's safe to say, many other players as well - and it's about time it got sorted out.