When you double-click to highlight a whole line and then drag the cursor, each line highlights in its entirety. That's the expected behavior. However a trailing empty line will not be highlighted at all, even though the cursor is clearly over that line. A copy will catch the endline from the previous line with text in it, but not that empty line. The expected behavior is that it is highlighted.
If you keep dragging beyond that empty line, it will become highlighted when the subsequent line is reached, even if that subsequent line is itself empty.
A minor thing, but bugs me every time.