I think you are doing something wrong with the zooming of the camera. If you scroll in one "tick" on the mouse wheel and then one "tick" back, it wont zoom out as much as it zoomed out.
Lets say you zoom in by 30%, setting it to 70% of what its currently set to. Lets say current_zoom = 50.
current_zoom * 70% = 50 * 70% = 35
Now you have to zoom back out by dividing by 70%, not multiplying by 130%.
35 * 130% = 45.5 // WRONG
35 / 70% = 50 // back to the original value, 50.
I hope i don't come off as rude, but i had to report this as its been bugging me since the game came out.
Happens on both linux and windows
Zoom in and then back out, you will be further zoomed in than you originally were.