The following steps illustrate the issue:

1. Open a new Writer document
2. Use "Insert->File..." to insert the file insert_this.odt (attached to this issue)
3. You can see that the list contained in insert_this.odt was inserted correctly
and the resulting document looks like this:
    1. List Item One
    2. List Item Two
    3. List Item Three

4. Now open another new Writer document
5. Press the "Bold" button (this is just an example; it works with other style
changing options as well)
6. Press the "Bold" button again to deactivate bold writing. Now everything
should be just as in Step 1, right? You have a fresh document containing nothing
with no style changes.
7. Use "Insert->File..." to insert the file insert_this. odt (attached to this
issue)
8. The result is that the list property of list item one got deleted and the
document looks like this:
    List Item One
    1. List Item Two
    2. List Item Three