Try the following:

1. Login with your SIP address in Lync 2013 for iphone or ipad. (mattias@kressmark.com)
Enter your password.
Click "Show Advanced Options" to enter your domain username (kressmark\mattias)
2. Logout by clicking the "Sign Out" button on the "My info" page.
3. Now change only the first part of your SIP address, but keep the domain part after the @ sign (billg@kressmark.com)
4. Click sign in - and you are logged on again.

The only difference is that after changing the first part of the SIP address you will see the
"Welcome. Let's begin..." wizard again.

Have anyone else experienced this?

Is it perhaps reported to Microsofts Support department already?

Hi,

Please install the latest update for lync client. NextHop is the Microsoft Lync Server teams customer response channel. You can give us feedback or propose and article topic by email at NextHop@microsoft.com.

Hi,

I am using the latest update 5.1 from July 29:th.

I will send an email to nexthop then, thanks!

/mk

This bug i also in the Android client I just noticed.