To be honest, It's basically just a side effect of the WASD controlling scheme. The aiming would definitely need some more work! But I just concentrated more on building the rest of the game.
The Gameplay is quite fun and very satisfying. Especially the fuel actually moving inside the tank is a nice change from the standard way of having a simple fuel display.
Just the background music is a little bit repetitive, a longer loop would have been nice.
A fun game. I liked the puzzles and that some even allowed for multiple possible solutions (although I'm not sure if that was always intentional). There were a few minor bugs that you explained in the description, but they were far away from making the game unplayable. Good work!