Inappropriate poo-ing - theories?

Hello
My 9 month old, Bling, has just started pooing in the bath tub 3 days ago. We haven't changed litter and I clean it daily. It's really strange.

He shares the litter box with my other cat but he's never had a problem before. And he's still peeing in his litter box (located next to the bath tub) - it's just the poo-ing we have a problem with.

I rearranged furniture a week ago but he seems to have adjusted to it.

Any theories on what to do or how to get him to use his box again?

Thanks

I've heard that some cats want one box for pee, and one for poo... also, if the litterbox is covered, could he be bonking his head when he poos? That may make him want to go somewhere else too . I'm sure someone will be able to help more than me- there are probably several good threads about it too- maybe someone can give you some links or you could do a search .