bad block found but data is still written into the bad block

[Alpha Root]

Hi,
I have a 2K page sized Nand flash, which has a bad block. The bad
block can be found by mtd driver:
Scanning device for bad blocks
Bad eraseblock 1513 at 0x0bd20000

However, when I try to copy file into the mtd partition, mtd driver
still writes data into this block. Then when I read back the file I
got I/O errors and the read fails. Does anyone know why this happens?

--
Bill