This is really odd...

I have the strangest problem with a ceramic mug and hope some of you potters can help me figure it out.

For the record, I have an undergraduate degree in 3D, with ceramics as my major BUT, I graduated over 45 years ago so I don't remember much and for various reasons I haven't done any potting since. At the time I was taking graduate level courses in glaze calculations and chemistry so I am not a complete novice however this has stumped me.

A few years ago I bought a beautiful coffee mug, made in Mexico but supposedly metal free, safe for the microwave, etc. I have used this mug everyday for years and all of a sudden last week it started smelling like cat pee. My cat had not been anywhere near it and I had just removed it from the dishwasher anyway. I washed it by hand and it still smelled, I put it through the dishwasher several times and it still smells. Tthe whole mug has this foul odor, inside and out. My family varified that it smells because I thought I was going crazy.

There are no holes, hollow spots or places where the glaze didn't cover all the clay. Does anyone have any idea why this would suddenly happen? I won't use it again but I am still curious.