Capital letters and Cisco RCC/Microsoft Lync

Yesterday i was working on a project that involves a new implementation of Lync 2013 and Cisco Cups.
We had enabled a user for RCC within Cisco and Lync, but the user was unable to register on the Cisco Cups Server.

The Cisco Cups is configured as a static route within Lync 2013, where it is used for a Cisco Sip domain called cups.contoso.com.

We configured the user using the following settings:
LineUri = TEL:3567;phone-context=dialstring
LineServerUri = %UserName%@cups.contoso.com (where %UserName% is the Sam Account name of the user).

[Get-csuser "alfa" | Set-CsUser -RemoteCallControlTelephonyEnabled $True -LineUri "TEL:3567;phone-context=dialstring" -LineServerUri "alfa@cups.contoso.com"]

After enabling the user for RCC, we saw that the Lync client of the user was unable to register itself within the Cisco Cups Server to enable RCC. We enable logging on the Lync Server/client, where we saw that the registration was canceled by the Cisco Cups server. Where the Snooper reported "Call Leg does not exist".
 We could clearly see that Lync ad Cisco where communicating, but at a certain point Cisco Cups sends a Cancel to the client in which the Client ends the communication.

The reason for the Cancel is still unclear, so we retrieved the Logs from the Cisco Cups server. There we saw that the Cancel was send after giving an unspecified error on the dial string. We verified the dialstring within Lync again and confirmed that it was set correctly. As we had no real clue as what was going on, a colleague retyped the dialString within Lync, but receive the notification that nothing changed. 5 minutes later the configuration started working. Upon investigating what had changed, we saw that the colleague typed the following LuniUri:    tel:3567;phone-context=dialstring. He had specified regular letters instead if capitals for the TEL letters. To prove if this was indeed causing the issue, we enabled another account for RCC where we also specified TEL in capital letters. The user was unable to register in Cisco Cups, after changing the letters to regular, the user was able to register and use RCC.

By psoting this encounter, I hope to spare somebody's time in troubleshooting this issue..