canon 1100d + canon 50mm/f1.8 front focus issue?

Hi,

I'm a beginner with DSLR. I bought Canon 1100D + Canon 50mm / f1.8. When I'm making family portraits with low aparture most of photos are not correctly focus. I'm using single focus point. I focus on eyeballs but picture is not sharp on the eyes but on shoulders or so. When I take photo in Live View mode problem seems to happen not so offen.

I made front / back focus photo tests.

Live view mode:

Viewfinder:

Is it problem in Lens, Body, Photographer ? Shall I return the lens back to shop?

Thx