Where did the Audio Selection icon go?

Running the Microsoft Lync courses this is an interesting bug in the Lync client that always comes up for discussion. Even if we have several audio devices and we can select which one to use through Tools / Options / Audio Device, the little audio selection icon that should be in the bottom left corner of the main Lync screen will not show up.

This holds true even if the client is updated to Lync CU6 (version 4.0.7577.4103)

This is a known bug described in the following KB article:
The Audio Selection Button is missing in Lync
(Article ID: 2616187)

Unfortunately the article reports: "there is no date that is available for a resolution." So, as a workaround for this problem we must enable Enterprise Voice for the user of this client:

Set-CsUser -Identity mattias -EnterpriseVoiceEnabled $true

Then the user must sign out, wait, and sign back in to the client, it is not necessary to actually restart the client. Once back in the client the little icon (and also the dial pad icon and call forwarding information) is visible again.