The last row is not fully visible when the gridview is scrolled to the bottom in case RowHeight is set to less than 20px. The less the row height the smaller the part of the last row which is visible. This is reproducible only in Office2013 theme.
The reported issue does not seem to be reproducible when GroupRenderMode is set to "Flat", which is the newer and recommended UI virtualization mode for RadGridView. If the recommended workaround does not meet the requirements you can try to change a FontFamily to be different from "Arial" and "Calibri" and FontSize to be different from 14 or open a support ticket.