A quick tip for anyone experiencing somewhat finicky buttons on a Vortex Sparc (Gen. 1): Chances are your unit isn’t defective, it’s just time to replace your CR2354 battery.
Apparently the red-dot will continue working until the very last moment, when your cell is completely out of juice – but the controls won’t. Sometimes they work, sometime they won’t. Turning the red dot on and off seemingly takes forever and occasionally won’t work at all. Even though the dot itself was as bright as it gets, turns out my battery was almost out of power. Replaced it with a new one – everything is back to working again like it’s supposed to.