I move the camera mostly via right-click + WASD, sometimes with [shift] if I want it to move faster. Occasionally, instead of moving my camera, it alters the draw distance / FOV / some visual aspect of the editing scene that causes trees and other object to disappear when I scroll enough, and eventually even the terrain starts disappearing. It is not m "zooming out". My camera does not move, the width and height of the FOV stays the same (one might say the depth is being altered though). What key am I hitting to cause this to happen, and is it possible to disable it?

^{side note: "keybinds" is probably the most spot-on tag for this question but it doesn't exist (surprisingly) and I lack the rep to create it.}