Switch the tape across as pictured above. It 100% worked for me. Put the old and new digitiser side by side and you will see the difference. I believe the metal frame makes a contact with the home button flex causing it to think it's always pressed.
I had the same issue and resolved it by re-touching my solder work on the home button flex ribbon - (the smaller set of joints that attach to the glass)
Move tape from old screen to new screen (near the home button flex, or use a non conductive tape to cover all the exposed circuits)
If its pre-assembled and the power button is not working, its either a bad solder or bad IC Chip (you can try retouching the solder, but if its under warranty I wouldn't mess with it unless its a last resort)