ECC check for Erased pages in NAND

I wanted to verify the following patch

https://patchwork.kernel.org/patch/8368341/

For same , wrote all zero's to one of nand partition :

nandwrite -n /dev/mdt1 < /dev/zero

But now when I dump this nand partition, see following errors:

 ECC: 3 uncorrectable bitflip(s) at offset 0x00000000
 ECC: 2 uncorrectable bitflip(s) at offset 0x00000800
 ECC: 2 uncorrectable bitflip(s) at offset 0x00001000

I thought above mentioned patch , suppose to fix this ECC errors but it didn't.

Is they other way to verify this patch ?