Sims 2 Stairs bug

Hi,

Stairs in the Sims 2 are bugging out, I am not sure if this has happened since the latest update as placing stairs before was okay.
What happens is I place stairs on the porch of a pre-made house and the stairs either disappear after a few minutes or they disappear but are still visible, yet I am unable to remove it and the sim cannot use the stairs. Please assist when possible as my sims obviously cannot access the house if there are stairs.

Thanks