That's exactly how Asacol works. The coating is what is special about it, because it won't dissolve until it reaches the ph that is in your colon, instead of dissolving in your stomach. And you can suck on them and they won't dissolve, either.
So when it comes out whole...it means your colon is moving things through too quick for it!
49 year old female attorney, diagnosed UC/pancolitis 1985, no surgery but much suffering.
Asacol/5ASA 6x400 mg maintenance for 20+ years; use prednisone & Rowasa for flares.
August 2008 sought care of naturopathic doctor. Food sensitivity test showed wheat/gluten, other intolerances; started diet without gluten, soy, dairy, tomato etc. Replete$$ probiotic powder, then Forte, now a stronger one (50 billion). Doing much better, but still having some bad days.