If I button all buttons except the top button at the neck (the way I wear them most of the time), a line often forms from the top most buttoned button to the shoulder, much like you see here (I apologize for not having pictures of this effect on my shirts. I might add some tonight if necessary.):
Now, if I button all the buttons, including the very top button (for example, if I were going to wear a tie), this line more or less goes away.
Incidentally, if I button all buttons except the top button at the neck and also unbutton the collar buttons (I would never wear it this way), the line also goes away or at least subsides.
Is this to be expected in a shirt with a button down collar?