John, it was I who gave that warning. There is a thread in the Over The Rainbow Bridge forum where a woman adopted a kitten only to have it pass away 4 or 5 days later. Right before the kitten died, she had found litter in its vomit and that the kitten was not urinating nor defecating. So that was the reason I passed on the potential warning.
Now when I got Tooties, she was about 6-8 months and had yet to go into her first heat. She had no problems with clumping litter but then, she was older.
My gut instinct says that it is probably safe now that Bob is 4 months old but as you said, keep an eye on him.
Btw, how long ago did you get Bob?