Did you BIOs mod these yourself or use the dual bios switch that XFX has? It looks like that is the core set via BIOS. My XFX 580's I just bought recently have Micron memory and using the BIOs switch the core is set to 1150mhz.
I'd noticed this too, but it's not consistent. Sometimes you can reboot and get the OC settings in SMOS, sometimes not.