can't see files after umount

I've downloaded and setup
newest yaffs2 sources on my kernel.
All is fine. I can do 
mount -t yaffs2 /dev/mtdblock3 /mnt/y
cp test1 /mnt/y
ls /mnt/y
    lost+found    test1

but after 
umount /mnt/y 
mount -t yaffs2 /dev/mtdblock3 /mnt/y

when I do  ls /mnt/y
I
receive only lost+found folder

I don't receive any warning/errors messages.
Can someone help me and recommend what to do?

Thanks.
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