Oops, I mean "Pet Talk, we have a problem

I need help from other multi-cat-households!!

One of our cats is acting weird . This morning, my hubby found his food-bag covered with cat-pee . He has a black nylon bag in which he takes muesli, yoghurt, bananas and apples to work. Yesterday evening he put it on the kitchen counter, near Maya's feeding place. This morning it was soaking wet, the pee even dropped down the counter onto the floor . I have NO idea who is doing this . In fact I found a smaller pee-spot on the same counter, closer to the window a week ago...! How the heck am I going to find out who did this????
The only cat who is acting a bit different is Maya: yesterday and the day before I saw her dropping her "poop" right in front of one of the litterboxes . No, the box was NOT filthy, as I change the filling regularly!

HELP !!!!