Than you for the details.I was able to see the issue in my env.
Please contact Quest support and open a case (please mention my name so I get the case).
I'm going to record the issue and I'll provide the reference number to you.
The issue will be addressed in future releases.
If your goal is make that field read only there is a workaround.
Use Form Component Behavior and Disabled When condition for this lookup field and set the condition as following
<Or><IsNotNull><FieldRef Name="Country" /></IsNotNull><IsNull><FieldRef Name="Country" /></IsNull></Or>
"Country" is the lookup column in my second list.
The idea is to make the condition always true so the field will be always read only.
Please let me know if you have any questions.