Stairs don't connect properly when placed upside down.
E.g. When 'upside down stair No.1' is placed next to 'upside down stair No.2' in the direction 'upside down stair No.2' is facing, 'upside down stair No.2 will connect, but turn to face the opposite direction of 'upside down stair No.1' (see screenshots 1, 2 and 3).
When 'upside down stair No.1' is placed next to 'upside down stair No.2' in the opposite direction to where 'upside down stair No.2' is facing, 'upside down stair No.2 will not connect at all (see screenshots 4 and 5).

PS. Screenshot 3 is taken from behind