Hello,
try to flash the image with "ubiformat" instead of "nandwrite". Because nandwrite also writes the pages that contains only 0xFF data and calculated ECC datas. UBIFS may treat the 0xFF only pages as erased and use them , but then OOB datas will be corrupted.
If you write the image with u-boot, try to use "nand write.trimffs" command.
For more details : http://www.linux-mtd.infradead.org/doc/ubi.html#L_flasher_algo
Also your NAND doesn't support subpage (512 B) writes.
Regards,
Sunay Mutlu