Strange kitty behavior

Question
About 3 years ago after I returned from a 3 day trip to Canada a came home to find one of my cats had pooped in my bath tub.  I was more baffled than upset and cleaned it up.  I figured perhaps the cat had been upset either because I had been gone so long or because the litter box had not been kept up.  I had my mom stop by when she could to feed them and change the litter, but not nearly as often as I'd had hoped.  I have several cats.  Some time later, however, it happened again, and so on ever since but only once a month if that.  The main problem is I am not sure which cat it is because I have never 'caught them in the act', but furthermore, I would like to know why they are doing this.  I thought maybe they are feeling unloved, or intimidated by the other cats.  Could it be a health issue?  I appreciate any advise and info.  Thank you.  

Answer
oh it could be anything. from not being happy about the amount of poop in the tub or just the sudden urge to need to poop while they are in the tub. if its once a month or so i wouldnt worry about it too much. if you are really worried, take the poop to the vet and have them analyze it. all they will do tho is look for worms.