OCS 2007 R2 to Lync 2013 conference attendant migration exception: cannot set region via Lync Control Panel

On a recent migration from OCS 2007 R2 to Lync server 2013, I run through an unexpected and, apparently, undocumented issue while migrating the OCS conference attendant.

I used the following command to migrate the only conferencing attendant, and result seemed OK

Move-CsApplicationEndpoint -Identity sip:Microsoft.Rtc.Applications.Caa-E55ADF4E-AFE5-4480-915C-694773F4CFA8@contoso.com -Target lyncpool.contoso.com

A detailed procedure is available in this excellent blog: https://www.simple-talk.com/sysadmin/unified-messaging/migrating-from-ocs-2007-r2-to-lync---part-3/  

To confirm that the number was migrated to the new pool, I checked the Lync Server Control Panel; dial-in entry was there, but got a warning stating no region was assigned to it.

When trying to assign the region via the Lync Control Panel I got this error:

Set-CsDialInConferencingAccessNumber : The region mappings for this access number are inconsistent.
I was unable to find any public resource with the error above.
Resolution was to assign the region manually via Powershell and using the -ScopeToGlobal switch

Set-CsDialInConferencingAccessNumber -Identity "sip:Microsoft.Rtc.Applications.Caa-E55ADF4E-AFE5-4480-915C-694773F4CFA8@contoso.com" -Regions "UK" -ScopeToGlobal

Note that, until a region is specified, dial-in might work but no dial-in access number is populated into the email template when creating a new Lync meeting through Outlook.