title: Custom lookup select issue
body: <p>The idea is to contruct a lookup with unique Employer name.
  The lookup works fine but when I select a value and then select the lookup button
  again and click on the place marked in <strong>RED</strong>, there are duplicate values, which is wrong.</p>
  
  <p>Kindly refer the snippet and snapshot </p>
  
  <pre><code>QueryBuildDataSource    qbds;
  Query                   query = new Query();
  FormStringControl       control = dialog.formRun().controlCallingMethod();
  SysTableLookup          sysTableLookup =  SysTableLookup::newParameters(tablenum(VendTable), control);
  ;
  
  qbds  = query.addDataSource(tablenum(VendTable));
  qbds.addGroupByField(fieldnum(VendTable,EmployerName));
  sysTableLookup.addLookupfield(fieldnum(VendTable, EmployerName));
  
  sysTableLookup.parmQuery(query);
  sysTableLookup.parmUseLookupValue(false);
  sysTableLookup.performFormLookup();
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/5gLY8.png" alt="enter image description here">  <img src="https://i.stack.imgur.com/A5MLK.png" alt="enter image descrip![enter image description here">tion here]<a href="https://i.stack.imgur.com/A5MLK.png" rel="nofollow noreferrer">2</a></p>