Selection Painting Issue

When selecting text by using the mouse to highlight a line via the left margin, the painting of the last line selected changes as multiple lines are highlighted.

Steps to reproduce:

1. Open the SDI Quick start.
2. Scroll until the last line (59) is visible.
3. Select the entire last line with the mouse by clicking in the line number area.
4. With the mouse still held begin selecting lines above the last and the last lines highlighted area will change depending on the number of characters in the top most line selected.