Buttons malfunctioning in PDF Viewer Widget Example

In the PDF Viewer Widget Example, the buttons that are used to go back to the previous view or to go forward to the next view are malfunctioning. They seem to remember the history of page numbers viewed across different documents, even considering different document sizes. If you changed pages in the previously opened document, you are able to use the "back to previous view" and "forward to next view" buttons after opening a new document without having changed the page number in the new document.

Observed behavior:

If the previously displayed document had 20 pages, and you went to page 17 at least once, you are able to repeatedly left-click the "back to previous view" button after opening the new document to go back to page 17, but this time displaying page 17 of the new document. Even if the new document has fewer than 17 pages, for example 10 pages, you are still able to go back to page 17, and in this case the page displayed is gray.

Steps to reproduce:

1. Open a document that is 20 pages long.
2. Notice that the "back to previous view" and "forward to next view" buttons are inactive.
3. Go to page 20.
4. Visit all pages from page 20 to page 1, going downwards.
5. Open a document that is 10 pages long.
6. Notice that the "back to previous view" and "forward to next view" buttons are active.
7. Repeatedly left-click "back to previous view".
8. Notice that the page count goes all the way up to 20, and that the page displayed turns gray when the page count exceeds 10.

Expected behavior:

The history of page numbers viewed should be reset when opening a new document. The buttons described above should be inactive after opening a new document, until you change the page number.