Open Radar

 
Summary:
I will describe the problem assuming that the Dock is positioned on the left side of the screen; the same problem also occurs when it is positioned on the right.

With the Dock positioned on the left side of the screen, it is very easy to move the cursor to the extreme left edge of the screen. (This is an example of Fitts's law.) However, while the Dock hugs the left edge of the screen, the click targets of the application icons seem to begin three pixels away from the left edge of the screen.

As a result, it is impossible to "throw" the mouse to the left edge of the screen, move it up or down to the desired application, and click. Doing so will not activate the desired application, but instead will click whatever is behind the Dock at that position on the screen—most often, the desktop. To activate an application in the Dock it is necessary to move the cursor to the right by a few pixels and then click.

This is a regression from previous releases of OS X and I believe that it is a serious usability issue.

Steps to Reproduce:
1. In the Dock preference pane, select "position on screen: left".
2. Move the cursor to the left edge of the screen. (This will show the Dock if Dock Hiding is on.)
3. Move the cursor upward or downward so that the Dock shows the name of an application other than the current one. Do not move the cursor to the right during the step.
4. Click.

Expected Results:
The application whose name the Dock is displaying, and whose icon the cursor is adjacent to, will activate.

Actual Results:
The activated application will be whichever one owns the pixel that was clicked on (excluding the Dock).

Version:
OS X 10.9 (13A603)

Configuration:
This occurs for me on a Late 2012 Mac mini and a Mid 2010 MacBook Pro 15". Both are running OS X 10.9.0.