Any application that prompts for a password appears grayed out

I upgraded from 14.04.5 to 16.04.1 on three different 32b machines. All of them have the same issue and it happens in several applications. For example if I attempt to update and/or upgrade the software, at one point the GUI prompts for the password. However it is grayed out and I can't enter the password. I found a way to enable that box by "rocking" to a different user and coming back to my username and then the password entry box will not be grayed out anymore.

I don't know what is the specific piece of software that presents GUIs for different applications.

So in a few words I expect to be able to enter a password but the box is grayed out.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: software-properties-gtk 0.96.20.4
ProcVersionSignature: Ubuntu 4.4.0-34.53-generic 4.4.15
Uname: Linux 4.4.0-34-generic i686
NonfreeKernelModules: nvidia
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: i386
CurrentDesktop: GNOME-Flashback:Unity
Date: Tue Aug 23 11:40:41 2016
InstallationDate: Installed on 2015-05-17 (463 days ago)
InstallationMedia: Ubuntu 14.04.1 LTS "Trusty Tahr" - Release i386 (20140722.2)
PackageArchitecture: all
SourcePackage: software-properties
UpgradeStatus: Upgraded to xenial on 2016-08-23 (0 days ago)