General Description: If the only constraints in a .ucf or .pcf are "TIMEGRP OFFSET" (no PERIOD, FROM TO, etc...) PAR doesn't invoke timing-driven operation. If the .ucf or .pcf contains a PERIOD, FROM TO, etc... the OFFSETs are then reported at the timing summary given at the end of the PAR job. TRCE always reports correctly, so this behavior seems to be unique to PAR.
This is only related to PAR. TRCE works correctly.