Townies are leaving cups, glasses, and mugs on pathways

I had this happen when City Living came out. There were coffee/tea cups all over the place. My Sim was just like 'Oooh free drink!'. I don't know how it got fixed that time, but I didn't do anything to fix it. I find right now that lots of cups and plates get put on walls that are not full height. If your Sim is getting the disgusting environment buff I find one of the reasons is that a cup is on top of a wall somewhere.