I made a basement that was made for nothing but nectar making/testing/aging. It was an outside basement, with the stairs being out of the house. It was a staircase with a width of 1. I made great-value bottles and decided to drink some of the bottles I had made. Also, I upgraded 2 of my 10 Nectar Makers to have Improved Pressing. When I wanted to pay the bills, the Sim walked up the stairs, then walked right down it again! It canceled the action that my Sim was going to do. I did many things to try to get him to NOT go down it after going up. I replaced the staircase, tried the Use Stairs and Go Here options, and nothing! I had to remove the staircase and use the resetSim action before it worked.
Why did my Sim go down the stairs immediately after going up it?