The red gridview pages at 5 items; the green gridview pages at 4 items.
The green gridview's total item count (12) divided by page size (4) divides evenly - each page has the same number of items.
The red gridview's total item count (12) divided by page size (5) does not divide evenly - the last page has fewer items than preceding pages.
Issues:
In both the red and green gridview, checking any row and then going to the next page will cause the same item on the next page to also be checked.
As a result of the previous item, in both grids, items not selected by the user are selected and included in the SelectedRowIds property.
In the red gridview (last page differs in length from others), when any item is checked and the last page is subsequently loaded, a javascript error is thrown on load.