For any of you who is interested in this issue. It seems that this is a bug with grub.
If I do the same thing with reiserFS on the USB-stick, everything works, but (at least) with ext2/ext3... it doesn't. I wrote to the bug-mailing-list from the grub guys,.. but it seems that they do no longer care for grub legacy... (what a support). Best wishes, Chris,
smime.p7s
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