Can add 2 Box colliders to cube
regression
- not present in 4.2.1 and 4.2.2
- present in all 4.3.x

2) How can we reproduce it using the example you attached
1 Create new project
2 Create cube - notice that Box collider added
3 Add another Box collider - the window "Replace existing component" appears - choose "Replace"
- notice 2 Box Colliders added

Expected: first Box Collider should be removed