I have to agree with nssg that your taper is probably a little on the fast side. Alot of people will experience some symptoms returning as you get lower in the doses. What we've done (daughter has UC) when symtoms have returned, we've upped the dosage back up. So if your were doing 40 mgs no symptoms and now are at 30 and getting some blood, up it to 35 mgs for a few days until the symptoms disappear. Then continue with your taper. I would suggest that you go slower. Don't taper by 10 try tapering by 5 mgs.
My daughter is tapering by 2.5 mgs. She is currently alternating between 2.5 mgs and 1.25 mgs. I think going slow is the key.
Also, keep a food diary to see what foods trigger your symptoms. And if you aren't doing so already, start taking Calcium with Vitamin D. Prednisone promotes bone loss.