When no lenses are enabled, and you click one from the list, it will reload the page with the lens enabled. But until the page reloads there is no feedback that it has enabled. So in that few seconds while its loading I often try to click the enable button, but instead it will now toggle off the now-enabled lens.
When clicking a lens from the list to enable, it should check the button client side immediately, before the page reloads.
