I mostly use thumbnails for browsing in theater view. When you're at the two bottom rows of thumbnails, there is little "glitch" in the programming I think.
Let me see if I can explain this well enough. Say you have 5 thumbnail columns width, and there is just one item on the last row. If you go down on column 2-5 to the second last row, the screen will not move the thumbnails upwards, showing the last row of thumbnails. In this case, the last thumbnail. So, you can be tricked into thinking that that row was the last, while there could be 1-4 more elements below!
A more graphical example:
Normal behavior (O is selection, and the ------ indicates the screen border)
X X X X X
X X O X X
X X X X
---------
Unwanted behavior
X X X X X
X X X X O
----------
X X X X
In these illustration it shows that the last row does not scroll up if there is no more items directly beneath the selection. And it can make people think that there is no more Artists, albums, movies, TV Shows or Episodes left. The only thing you CAN do to be sure, is to press the down button again, to see if the selection moves to the last row. This makes it very easy to go directly from the bottom to the top though. Which you might not want.
I hope that you can change this behavior so that the screen updates with the last row even if there is not any items directly beneath the selection. Check if there is another row instead perhaps?