It would certainly explain how my friend yesterday used up 250 shells in a matter of a few minutes yesterday in multiplayer. Seems like marking a target should fire only one shell, though. Or enough shells to guarantee its destruction based on artillery damage?
Unless someone else can show that it's happening outside of your game I'm not seeing anyone else have the same problem. The game also has specific logic in place to only fire once t artillery in the base game so I still suspect your mouse is simply clicking extra times or the artillery is firing at nests/worms in automatic mode.
If you want to get ahold of me I'm almost always on Discord.
Was repeatedly starting new games while doing some mod work just now (restarting Factorio every two minutes is fun!) and one of the times I clicked "Start" to generate a fresh map and start the freeplay, I heard the click sound effect three times.
It only happened when I clicked by tapping my MacBook Pro's touchpad. Infuriatingly, I was unable to repeat the behavior after the first occurrence.
In my case, it could be an intermittent issue with the Boot Camp touchpad drivers under Windows 7. But it doesn't seem to be a bug in Factorio itself.
silergerma, what environment are you playing Factorio under? What OS on what hardware? What pointing device do you use?