MY male is doing the same thing. Only it started befroe the Holidays. When he's going to do it it is always in the same place..... the right side of the toilet! He does this maybe once a month.
Their litter box is cleaned everyday. I can't figure it! I guess pooing in the bathroom is better then urinating at random spots in the house! If you can come up with some kind of reasoning for this.....let me know!