incremental compile post fit netlist status NA

i have several design partitions in a 530GX. i'm trying to preserve the design paritions using the post-fit netlist. after i finish i compile, in the design partition window, i see valid dates for "source" and "synthesis" partitions but my "post fit netlist status" is not available.

why would my "post fit netlist status" be "not available" after a full compile of the design

thanks

ken