[Yaffs] NAND page in a file was overwritten with 0x00

Hi,

on one of my devices a 2048 byte section in a file was overwritten with 0x00.
The file is never opened for write access (it's the dhclient executable).

Also the 2048 bytes are exactly the size of a flash page:
mtd_debug info /dev/mtd1
mtd.type = MTD_NANDFLASH
mtd.flags = MTD_CAP_NANDFLASH
mtd.size = 526385152 (502M)
mtd.erasesize = 131072 (128K)
mtd.writesize = 2048 (2K)
mtd.oobsize = 64
mtd.ecctype = MTD_ECC_NONE
regions = 0

So far actually I have no idea how this happens. Any ideas?

Mount tells me there is a bad block on the device:
<7>[ 126.952083] yaffs: checking block 3197 bad

May this be related? And is it possible to check on which NAND block a file is
saved?

Best regards
Thorsten

PS: I already had a similiar problem with another device and some other file
but I did not pay much attention to it. So this is at least the second time
this happens to me :-(