Yes I have, and yes - every single time I boarded at KGX I'd invariably pick one of the two center coaches, then notice the smell, then move to an end coach. Every time I boarded anywhere else, the train was already too full to move (but I usually had more luck remembering which coach to pick). It's my main memory of the unit. (The smell did get less bad the further you went from the toilet, but it was still noticeable in the entire carriage - and it seemed the smaller toilet was the worse one for smell.)
I see people are rather touchy about their trains here...
(Just to be clear I'm talking about the toilet chemical smell, not the excrement smell. It's somewhat similar to urinal smell.)