Kerbal Space Program

What happens: The vessel can quite easily be placed outside the build-pad and even save in this position.

How to reproduce:
Step 1: Create a new vessel and place anything on it as you see fit.
Step 2: Tilt the camera up so that the viewing angle is looking down on the build-pad.
Step 3: Zoom out a little to make it easier to reproduce.
Step 4: Click on your command unit to select the whole vessel and drag it all the way into the ground.
Step 5: While it is in the ground, drag all the way either right or left of your screen and left-click to release it.
Step 6: Rotate the camera until you find the buried vessel and click on it to pick it up.
Step 7: Now rotate the camera around and watch your vessel fly off the screen.

Notes:
You can place your vessel off screen and it will even save it there if you want.
It is possible to place your vessel below the ground surface, but it is not possible to place your vessel through the ceiling.

Solution:
Create a boundary around the VAB.