Minimap is auto-zooming

Sometimes when I hit hotkeys in normal gameplay, the mini map/overlay map will change to fully zoomed in, or fully zoomed out. It has happened with all the normal ability hotkeys, the flask hotkeys, and even the tab key to switch the map types. In the UI screen, the bar moves from min or max when this happens. I can always change it back to where I want it manually, but id like the randomness to stop. This has been going on for me for years, so its not a patch or expansion specific issue.

Are you sure you didn't hit +/- somehow ?

(Also, weirdly, map zoom in / out doesn't seem to be rebindable ??)

100% not hitting +/-. It happens when i hit W, which is my movement skill. I usually have left click down at this time as well. not sure if that helps.