Quick answer: Unity RectMask2D visually clipping children but raycasts still hit clipped regions? Clipping is render-only - add a separate Image with Raycast Target to block input.
Scrolling list shows truncated rows. Clicking on the empty space above the list still selects the clipped row underneath.
Use a Mask instead
Replace RectMask2D with a Mask component. Mask intercepts raycasts at its bounds; RectMask2D doesn't.
Or add a raycast-blocking image
Place a transparent Image above the list, sized to match the visible area. Raycast Target on; alpha 0; no Image graphic needed.
Toggle Raycast Target on clipped rows
For dynamic lists, set raycastTarget = isInsideViewport per row. More CPU per frame; fewer ghost clicks.
“RectMask2D is a render optimization. Input layering is separate.”
Use the Inspector's Raycaster Debugger overlay (Scene view > gizmos). Visualizes hit targets so phantom interactions are obvious.