[Yaffs] Some incomprehensible points with yaffs2

Hi,
I have tried to use yaffs2 from the last android's fs/yaffs directory with
2.6.24 kernel.
And I have some problems with it.
There is jffs2 on first partition (mtdblock0), which works well enough. From
it I try to erase second partition (mtdblock1) with flash_eraseall tool and
copy necessary boot files there. Then I try to boot from second partition
and system booted well. After several reboots (or some operations with
files) yaffs2 looses capability to restore from checkpoint and i can see
tragedies, such as:

yaffs tragedy: Bad object type, -409329664 != 1, for object 512 at chunk
33931 during scan
yaffs tragedy: attempting to use non-directory as a directory in scan. Put
in lost+found.
yaffs tragedy: attempting to use non-directory as a directory in scan. Put
in lost+found.
yaffs tragedy: Bad object type, 2 != 3, for object 277 at chunk 293 during
scan
yaffs tragedy: Bad object type, 2 != 3, for object 265 at chunk 269 during
scan

In most cases system is bootable after that, but yaffs2 can't restore from
checkpoint any more. If i only try to reboot errors may stay in this state
(i see identical numbers of chunks etc.) and system is bootable. After some
experiments with file operations (add/remove) or turn off power with out
umount root fs, files/directories started to vanish after next reboot. And
in one try system is able to boot, but in anther it cant find some system
file. I cant detect clear dependences.
When i look at checkpoint debug logs, i see that (when yaffs try to restore)
first checkpoint block it reads without any errors and (in most cases)
second checkpoint block is not correct (i think so, because it isnt idential
to writed data) and restore process interrupted. In what direction i have to
research ?
And maybe silly q, i copy 21 mb dir (~3k objects) from jffs2 partition to
yaffs2 patition and get 77mb on yaffs2 partition is it ok?
Sorry for my English, Lebedev Dmitriy.