debug messages of unknown origin

some scripts from Example/scatter2d (CorrelatedRoughness.py, FindPeaks.py, GratingMC.py, RectangularGrating.py) generate lots of debug output like

...
DEBUG x=2.86297 -> i=25
DEBUG x=0.548277 -> i=64
DEBUG x=0.548277 -> i=64
DEBUG x=2.86297 -> i=25
DEBUG x=2.87165 -> i=25
DEBUG x=0.556957 -> i=64
DEBUG x=0.556957 -> i=64
DEBUG x=2.87165 -> i=25
...

I have not yet found out where these messages come from.