Drag a button onto the stage.
Select the layout tab.
Click the background of the tab to give it keyboard focus (it should already have keyboard focus but there is a bug outlined in DTL-3461).
Now hit the tab key - the leftAnchor field should get focus (don't edit the value).
Hit the tab key again - the leftAnchor checkbox gets focus AND changes state to true.

I don't think we should change the state of checkboxes when they get focus. How do we know that is what the user wants? They are just as likely to be using the tab key to traverse to a property that is further down in the panel.

I understand that in this case we "help" the user by checking the box when the anchor value is edited. That is ok. But in all cases, the state of checkboxes should never change just because they get focus.