I loaded stacks of 12 cobblestone into the 3x3 grid of my crafting table to craft stairs. I expected to get stairs each time I click in the right most crafting box that shows the stair and that each stack in the 3x3 grid should decrease by one.

What actually happens is that as I collect stairs, the count remaining jumps to 10, then increases each time I pull another set of stairs from the crafting box. The values I got were: 10, 18, 34, 66, 130, 258, 514, 1026, 2050, 4098, and 8194.

It does end up stopping when the appropriate amount of stair is crafted and the remaining cobblestone should be 0, but still shows the highest number reached in the 3x3 grid.

Easily repeatable.