Photoshop CS: "Append Metadata" with file browser

Hi.
1. I did a metadata set in Photoshop CS (8.0.1) including keywords and
description and saved it.
2. I select image files in the file browser that already have some
keywords and descriptions.
3. I use file browser's command "Edit, Append metadata" (not "Replace
metadata").
Result:
The existing keywords do remain, new keywords are added. That's what i
expected.
But: The existing descriptions go overboard, only the new description
stays in the images.
Questions:
Can i automatically append a new description in a way that the old
text stays there, too?
Is the original description generally deleted if i use "Append
metadata"?
Does this make sense, or is it a bug?
Thanks for all your first-hand experiences!