RATE not determined in RATE DETERMINATION also getting fetched.

Hello ISU Gurus ,

I have an Installation say INS1 with Rate Category XYZ and to this Installation 4 Devices are connected Each with Individual Rate types ( Say ABC1 , ABC2 , ABC3 , ABC4 ).

Now Rate Determination is maintained for the above Rate Category + Rate types combinations i.e

XYZ + ABC1 = RATE1

XYZ + ABC2 = RATE2

XYZ + ABC3 = RATE3

XYZ + ABC4 = RATE4

Now  a Billing Schema is defined say BLLSCHM which contains of the above Rates i.e RATE1 , RATE2 , RATE3 , RATE4 and also RATE5 ,

Now for RATE5 No Rate Determination combination is available in this particular Installation , though this installation INS1 refers to Rate Category XYZ and XYZ indeed refers to Billing Schema BLLSCHM which contains RATE5.

Now my question is whenever I am doing Billing , the Billing Document generated contains Line Items generated due to RATE5 also , how is this possible ? reason being No Rate Determination is maintained for RATE5.

Please help me getting clarified with the same.

Thanks ,

Sijin