Enable CONFIG_MTD_NAND_VERIFY_WRITE?

Hi,
Is the mtd CONFIG_MTD_NAND_VERIFY_WRITE necessary or YAFFS do some write 
verification itself?

If I enable CONFIG_MTD_NAND_VERIFY_WRITE I got some error message like this:
nand_write_oob: Failed write verify, page 0x0000e000

I added some more print messages and I discovered what yaffs tried to 
write (on the left)
and what read back from nand (on the right)

0: 0xff <--> 0x00
1: 0xff <--> 0x00
2: 0xff <--> 0x04
3: 0xff <--> 0x00
4: 0x00 <--> 0x00
5: 0xff <--> 0xff
6: 0xff <--> 0x00
7: 0xff <--> 0x42
8: 0xff <--> 0xff
9: 0xff <--> 0xff
10: 0xff <--> 0xff
11: 0xff <--> 0xc0
12: 0xff <--> 0x64
13: 0xff <--> 0x9a
14: 0xff <--> 0xa9
15: 0xff <--> 0x9b

I suppose it's the correct behaviour when yaffs delete a chunk with 
yaffs_DeleteChunk().
Can you confirm it's the correct behaviour?
What do you suggest to do, disable CONFIG_MTD_NAND_VERIFY_WRITE or path 
the nand_base.c file in mtd?
I really need some sort of write verification.

I'm using yaffs in yaffs1 mode with a 32MB Samsung small page nand flash 
and uClinux 2.4.31 with a
patched version of mtd (based on 4/03/2005 CVS mtd)

YAFFS built:Dec 28 2005 12:45:50
$Id: yaffs_fs.c,v 1.38 2005/12/15 20:27:56 charles Exp $
$Id: yaffs_guts.c,v 1.27 2005/12/20 04:02:18 charles Exp $

Device 0 "Yaffs Data"
startBlock......... 0
endBlock........... 255
chunkGroupBits..... 0
chunkGroupSize..... 1
nErasedBlocks...... 251
nTnodesCreated..... 100
nFreeTnodes........ 94
nObjectsCreated.... 100
nFreeObjects....... 95
nFreeChunks........ 8056
nPageWrites........ 74
nPageReads......... 74
nBlockErasures..... 0
nGCCopies.......... 0
garbageCollections. 0
passiveGCs......... 0
nRetriedWrites..... 0
nRetireBlocks...... 0
eccFixed........... 0
eccUnfixed......... 0
tagsEccFixed....... 0
tagsEccUnfixed..... 0
cacheHits.......... 0
nDeletedFiles...... 0
nUnlinkedFiles..... 0
nBackgroudDeletions 0
useNANDECC......... 1
isYaffs2........... 0

Regards,
Claudio Lanconelli