Vertex Snapping problem : the cursor doesn't move

Hello everybody!
I am using Unity 5, and try to use the Vertex snapping function.
I do as it is said on the site : select the cube I want to move, press V, select the vertice I want to move, while still holding V, but when I try to move it towards the vertice of another cube, it doesn’t work : the cursor doesn’t get out of the initial cube.
What do I do wrong?
Thank you very much for the help, and sorry for the bad English!

Not sure what is going on for you. It works perfectly here with two cubes a few units apart from each other, and also with a third sphere a few units away. Everything snaps properly, Unity 5.2.1f1.