Hi Martin,
if even IS_OVERLAPPING is not called this means either that the data slice is not active (sorry) or you have the following situation: The data slice is defined e.g. for 3 characteristics A,B and C but in the aggregation level you use only B,C and for A in the data slice the flag '# is used' is not set. In this case column for A in the returned records would be '#'. The flag '# is used' not set means that the data slice is not interested in '#', thus it is not relevant.
In a MultiProvider or CompositeProvider the above situation may also happen if A in the MultiProvider or CompositeProvider has not assignment to the part provider with the data slice.
Regards,
Gregor