replaced the battery and the lock button is now not working / working

Hi guys. I am having similar issues. I replaced the battery on my iphone 5 and the lock button is now systematically not working / working. If my phone goes to standby and the screen goes to black for a long while, the lock button will work once. Then it refuses to work until the phone goes to standby again for a long while.

I've inspected the jumpers and they seem intact. Here's the photo.

http://just1ed.files.wordpress.com/2014/...

Can anyone help? Is it worth giving the lock button flex cable replacement a try?