MarkSpeckles maxPixDiff behaviour

IPP18.1

Microsoft Visual Studio 2015

Does any body understand how the maxPixDiff paramter works in the markSpeckles function?

Using the test image below I expected that for the image

- threshholded at 8194

 - maxSpecklesSize of 300

That a maxPixDiff value of >25 would include the 'blue' (middle ring value 8240) portion of the image  however

- setting the value to 24 finds the centre portion as expected

- setting 26 finds NOTHING (not even centre portion)

- setting 80 finds NOTHING (not even centre portion)

Note this behaviour is evident on other images (actual data) not just this test pattern

Any help understanding this would be appreciated