In the app builder application, when applying a filter using the "is not" condition yields wrong results. It works exactly how "is" works. For example I have A and B entries in the field and I say filter this field and show what "IS NOT" A. It should show me only the B entries in the map but it does the opposite. If I try to use the condition "is" it again shows the A entries which is correct in this case. So "is" and "is not" yield the same results.
I tested it in the web map and it works correctly there, so I guess it is a problem with the web apps.