Operating system and graphics card
Broken: 2.72b and before
Short description of error
After scaling up the objects, the vertex coordinates, which was in the same point of space (snapped one to another) appear to be in different coordinates.
Exact steps for others to reproduce the error
Add two cubes, move one of them to random location, then snap another one to it. Scale them *100. Check the "shared" vertex coordinates of the second cube.
If I will export the scaled cube (for example to collada file), I get broken uv unwrap because of the same issue, i think. All polygons will be detached one from another.