I'm playing on a Mac, and wanted to be able to zoom with my mouse when using various ranged weapons, so I set it to 'q' to zoom in, and 'tab' to zoom out. It was originally set to 'mouse+,' whatever the heck that means.
So, I went ahead and found a zombie, took out my bow, and pressed 'q' to zoom in. Then it was that I discovered that the game seems to have gotten the words 'zoom' and 'scroll' mixed up, because my vision/sight/crosshairs didn't zoom in like every other game does, but instead, the selected item on my hotbar just scrolled to the left until I stopped holding the button.
The right mouse button still zooms like it did before I changed the hotkeys and how you'd expect it to work. But like I said, I'm using a Mac, and while Apple stuff is typically pretty great, a mouse that you can't use both sides at the same time is a trashy mouse.

My friend gave me this game today, and I don't even know how to get mods, since there's no steam workshop. The only other problem I've had with the game so far is that medium graphic settings are too high for my computer : P