innovus saveNetlist issue (UPF_IS_1)

When I saveNetlsit in my innovus , I found Some PG nets which connected to std cell PG pins have been renamed ,  from VDD to VDD_UPF_IS_1, in netlist it shows like:

.VSS (VSS_UPF_IS_1)

.VDD(VDD_UPF_IS_1)

it should be 

.VSS (VSS)

.VDD(VDD)

I don't know the reason,  Does My UPF  conflict with my database Globalconnect ? 

Thanks