I've had this happen for years, and it's perfectly okay and expected. It's actually in the side effects or other notes in the packaging info for Asacol. For me, it happens with and without flares, and I don't feel a difference in how my treatment is working. It's not an everyday experience, but it happens more often than one would expect. Hope this puts your mind at ease! And don't hesitate to call your doc if you're really worried about your dosage.
Actually, in the package insert it says to tell your doctor if this happens repeatedly.
I've noticed mine coming out whole lately, too. It seemed to happen more often when I started flaring worse a few weeks ago. Almost every day I notice the red casing, but I have been seeing the white medicine inside pretty often lately.