How a DOM parenting bug silently broke pointer events behind a fixed overlay

A developer building a crop overlay with draggable handles discovered that position: fixed visually lifts an element but does not remove it from the DOM tree, leaving event routing unchanged. The crop overlay was a child of a canvas stage element that called setPointerCapture during pan gestures, which redirected all subsequent pointer events to the stage after the first move. This caused the overlay to receive exactly one pointermove event per drag before going silent, a subtle signature pointing to pointer capture rather than a broken handler. The root cause was the assumption that fixed positioning creates an event boundary, when in reality it only affects layout and paint. The fix required either restructuring the DOM so the overlay sat outside the capturing ancestor, or explicitly releasing pointer capture when a drag begins on the overlay.