Appears to happen after getting -EIO on read of /proc/ide/hdc/media (see bug 139923).
Had exactly the same problem. Two SATA drives (sda, sdb) and IDE CD-ROM (hdc). Installing kernel-2.6.9-1.724_FC3 solved the problem of reading /proc/ide/hdc/media (as described in bug 139923), so I'm not getting core dumps anymore.