Unable to install signed encryption certificate from E-Mail on IOS 8.1.2

I am no longer able to add a user's signed E-Mail certificate after upgrading to IOS 8.1.2. When you clicked on "install," nothing happens.

It should change the icon to "remove" and add the user's signature encryption certificate for future Encrypted E-Mail to the same user. (See below link for how it normally works.)

The signed certificate was originated from an MS Outlook based E-Mail. Anyone else experiencing the issue? Thanks in advanced.

iOS: Using S/MIME to send encrypted messages - Apple Support

To install and trust the sender's signing certificate, tap Install.