I have just updated from Gimp 2.6.4 to Gimp 2.6.5. The UI changes look good, but the new checkbox handling is very confusing: on mouseover, the checkbox displays *the state it would have when clicked*. This means that the displayed state with the mouse over the checkbox is exactly the opposite to the current state. With the mouse over a currently deselected checkbox or its label, it is displayed as checked; clicking the checkbox (selecting the underlying value) immediately changes the displayed state to unchecked. The correct state is only displayed when moving the mouse away from the checkbox and label. I find this very confusing, and have made mistakes as a result.
Example: select the crop tool, and watch the behaviour when changing the settings "current layer only" and "Allow growing".