It is just case story. 
I had got a report with IP results for interpretation. 
Field data from report
One line with IP anomaly from Report. The pictures quality was very poor.
Field data in x2ipi
Same line in x2ipi (reference point is MN center)
Measured voltage
Left lower corner is blanked since values of apparent resistivity are less than zero. The measured voltage there is less than 1 mV.
Measurements with identical IP decay curves
Let's look at IP decay curves. They are the same for some readings.
Identical values in field data table - Copy-paste results
Identical values in the field data is a result of Copy-paste. All results with a negative IP have been replaced by measurements from another part of line. The data table confirms this conclusion. It is just cheating.
This results in that the interpretation of such data is impossible.

This case shows how important it is to analyze field data before interpretation.