Power button stuck after rear case replacement

I'm changing iPhone 5S rear case, but for some reason power button does not seat properly in its place during assemble. It's stuck and I can't push it. Button doesn't move at all. I have watched it very closely so that everything is in the right position, and I just can't find what is wrong.

Hinge of the power button bracket is on its place, orientation of the button is correct, I have moved this little round metal plate from the old button to the new one and also the little black dot is still on its place on the top of the cable.

I tried to search this with Google and from this web page but couldn't find anything. Does anyone have had this same problem? This is already the second time I have encountered this problem. Is there some easy trick to get this fixed or what? I just can't figure out why this power button gets stuck every time I try to replace it.