Russell, I have the same problem in Acrobat 9.0. Have you learned a fix yet?
This is a bug of Acrobat 9. This has not yet been fixed, I think. I also struggling for a solution. I have a feeling that Acrobat programmers do not know to fix this bug! I have reported this bug many times at adobe web site.
I can't believe that Adobe still hasn't fixed this problem. One workaround is to extend the thumbnail window to make the last row show the same number of thumbnails as the rest of the rows. I have noticed that if the number of pages divided by the number of rows displayed = a whole number then the last row will display. For example, a 1746 page document will show the last row of thumbnails with 1, 2, 3, or 6 rows showing. The last row will not display if I have 4, 5, 7, or 8 rows of thumbnails showing. Another example is a 295 page document. To display the last row of thumbnails in this document you would have to display either 1 row or 5 rows of thumbnails as these are the only numbers that when divided = a whole number.The number of pages divided by the number of thumbail rows displayed must = a whole number to display the last row.
If there are a small enough amount of pages, though, you can make the thumbnails small enough to display all of them in the window and this won't be a problem. You can also add a blank page at the end of the document temporarily to increase the number of rows you can show to display the last row but this isn't always possible.
Hope this helps!
This has been an issue since the first release of version 9 and I guarantee there
have been numerous bug reports on this issue. I offered a valid work
around until Adobe decides to fix the problem. Adobe is well aware of
the thumbnail problem, trust me.