Yup, this happens - as happened at my place in spring as well.
You should definitely fix these problems if you'd like to keep your
things nice and tidy.
To erase the old snapshot and terrain,you have to "Unlock" them first
(Edit menu). Then you can safely import the new terrain. Make sure to
follow these guidelines to "update" your existing models instead of
uploading them as new ones (thanks Matthias and Lemastre):
http://groups.google.com/group/SketchUp/web/faqs-for-using-the-3d-warehouse
In any case,while uploading and the already entered data (like
description) does not appear,you are doing something wrong.
Gai...