Firefox-Scrolling Rows

Using Firefox 1.0.6, using the paging workaround with the grid. When paging to page 2,3, etc. the background color appears on all rows, then disappears on the last 5 or so rows (20 rows on each page). When you move the mouse over the rows, they shrink over top of each other towards the top. If you move the mouse back to the bottom the rows follow the mouse & the grid returns to normal. Any suggestions?