The top portion of the selected rows has a background image, while the bottom one has a background color. You must change one of the two to match the other one. Alternatively, you can remove the background image completely for selected rows (look for the rgSelected CSS class).
As to your second question, I am not sure what causes the discrepancy and will need a runnable demo. Have you tried using Firebug to figure this out?
All the best,
the Telerik team