Nexus 4 Nav soft-keys not responding
I used Nexus Root Toolkit on my Nexus 4 with Android 5.1.1. Here's what I did:


Rooted my Nexus 4
Launch &rarr; Fastboot Flash &rarr; Recovery&rarr; Latest CWM
It installs Quick Reboot app in your Nexus 4. Open it and "Recovery" will reboot your device in recovery mode. If it asks for root permission, grant it.
Install zip &rarr; Install zip from sideload
In Nexus Root Kit &rarr; Advanced Utilities (Click on Launch in NRK) 
Launch CMD Prompt
It will show you the path of current location. Copy the correct UPDATE.zip (download).
In your device, enter the command adb sideload UPDATE.zip.


That's it. Go back and reboot your device.

Enjoy!