title: count distinct of text field in data studio increased when using filter
body: <p>I want to count the number of sessions with a certain event label in google data studio. I have created a new field in data studio on a google analytics source like this:</p>
  
  <pre><code>COUNT_DISTINCT(CASE WHEN Event Label = "Form Start" THEN Session ID ELSE "" END)
  </code></pre>
  
  <p>where Session ID is a custom dimension from GA (string). 
  The problem is that when I for example pull this new metric to a scorecard, I get a value of 6, if I then add a filter on this scorecard with Event Label = "Form Start" (the exact same event label as in the case statement of the new field) the metric is increased to 23! (which is the correct number).</p>
  
  <p>Is there some data truncation going on in data studio behind the scenes or why does using the filter increase the distinct count?</p>