When searching using the column headers on the list against a boolean type field such as the 'Active' field found in an OOB instance, the results returned do not match what users may expect. So if the user types in just "true" on the column header search, they will see results where the value is showing as "false" instead of "true".
returns NULL causing what is most likely going to be "false" results.
This is by designed and is expected behaviour since the system defaults to either 'STARTSWITH' or 'CONTAINS' operator depending on the property configured.
The results will return a NULL value which shows "false" values.
It should be noted that the ability to do 'STARTSWITH' or 'CONTAINS' within the search filter builder is not available.
If intending to use the column search, it should be written as either "=true" or "=false"