Windows, when Illustrator isn't focused, clicking inside the window, the click is lost, another click is needed to perform the intended action. Annoying, because the second click is treated as double click.

To reproduce:
Open Illustrator and move the window to the left. Open another program, for example a text editor. Clicking in the illustrator window over a text (with the intent of copying the text causes just focusing the window, the text itself isn't selected. Only the second click selects the text.