A problem with transparent material,A problem with trasparent shader

There are 2 cubes in the scene with standart mateial with transparent rendering mode
And when a small cube is right in the middle below big cube it works fine in any angles like in the image:[148143-снимок-экрана-31.png|148143]

But when I a little translate the small cube xAxis in some angels it starts to look strange, although I didn’t change materials and cube positions:
[148144-снимок-экрана-32.png|148144]

So why in the second picture in some angles of camera the lower cube looks as if it above big cube and how can I fix it?

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Please read the very thorough answer here: