The LS1021A NAND driver provided in the QorIQ Linux SDK does nor report bit flips when bits are flipped in a sector of page. This applies both to U-Boot and Linux driver.
E.g. the following u-boot command returns OK while page 3fe000 contains an uncorrectable number of bit flips:
=> nand read 81000000 3fe000 1000
NAND read: device 0 offset 0x3fe000, size 0x1000
4096 bytes read: OK