From the deployment screen, orders designating a target ship can “freeze up.” Assign an escort, formation, or protector order, then click on the background, not on a valid target. The ship assignment line vanishes, but no target is assigned so “Ok” remains grayed out. Clicking “Set target” has no effect. This is annoying on very large maps, where it’s easy to miss your target when trying to tell fighters to escort a frigate not much bigger than a pinhead!
When the UI is turned off in battles (after pressing U), tooltips still display when the (invisible) cursor is positioned over a ship.