I am experiencing some odd issues with the List Lookup control in Nintex Forms.
It appears that if you create a new form for a list that utilizes a single line of text field to store List Lookup values, the List Lookup Control does not display the current value stored in the field. Is this expected behavior?
It also appears that if a workflow changes the value in a single line of text field that was previously set by a List Lookup Control in a Nintex Form, the value does not change in the List Lookup Control. It retains the original value set in the form until you open the form and save it. Is this also expected behavior? It doesn't seem as if it should be. I was able to do this without issue when using InfoPath forms. Not sure why there is so much trouble in the Nintex Forms.
i would suggest if you don't want this changeable in the form that you use a calculated control that does the list lookup and connect that to the column you want and make sure that the calculation happens on new, edit and display modes?