<hr /><i>oehhar added on 2018-05-14 15:00:15 UTC:</i><br />
Well, after the intense help of Rolf, this point is fixed in checkin [300b2b5c3a].

I get the following result for the initial test script (running 10 minuites on my computer ;-)) :

<verbatim>
  Full Extent:
{} {XMin {{} -8883833.3022622615} YMin {{} 4916395.3269803952} XMax {{} -7973800.0204237271} YMax {{} 5632483.3843831643} SpatialReference {{} {WKT {{} {PROJCS["WGS_1984_Web_Mercator_Auxiliary_Sphere",GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137.0,298.257223563]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Mercator_Auxiliary_Sphere"],PARAMETER["False_Easting",0.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",0.0],PARAMETER["Standard_Parallel_1",0.0],PARAMETER["Auxiliary_Sphere_Type",0.0],UNIT["Meter",1.0],AUTHORITY["EPSG",3857]]}} XOrigin {{} -20037700} YOrigin {{} -30241100} XYScale {{} 148923141.92838538} ZOrigin {{} -100000} ZScale {{} 10000} MOrigin {{} -100000} MScale {{} 10000} XYTolerance {{} 0.001} ZTolerance {{} 0.001} MTolerance {{} 0.001} HighPrecision {{} true} WKID {{} 102100} LatestWKID {{} 3857}}}}
</verbatim>

Kevin, I would appreciate a test and review within one week.
No test is ok to, I will merge and close.

Thank you,
Harald