Simple selection: where field_name is not null. Notice I have the 'show all fields' button active.
But <null> appear as selected and it does not matter if I have show all records or show selected records active: they all appear as blue, selected. The number of selected records seems correct: emphasis on 'seems'....
When selecting for 'IS NULL', those records that are null don't show as selected when 'show all records' is active:
Again, the number of selected records 'seems' to be correct. If I toggle to 'show selected records' I get the correct selected records (no 'is not null' records are 'blue')