Quick answer: Godot 4 Control input not registering when the Control is inside a stretched parent? Default mouse_filter = STOP intercepts events for the Control's rect but stretched parents may not size correctly.
Button inside a VBoxContainer with full_rect anchor doesn't click in the lower half of the panel.
Verify Control sizing
Run with Visible Collision Shapes. Control's actual rect should match the visible button. Mismatch = layout bug; fix the parent's container behavior.
Set mouse_filter explicitly
For interactive children, MOUSE_FILTER_STOP. For overlay decorations, MOUSE_FILTER_IGNORE. Default is ambiguous.
Test at multiple sizes
Run the scene at min/max screen sizes. Layout-sensitive bugs surface at boundaries.
“Control rect determines hit testing. Parent layout determines child rect. Both must agree.”
Build a UI debug overlay that draws each Control's hit rect. Saves discovery time when a button mysteriously stops working.