official systemrescuecd-x86-4.9.0.iso has following checksums:
when installed with app-admin/systemrescuecd-x86-4.9.0 iso file does not match with above summs.
moreover, if i do re-emerge, checksumms are different with each rebuild.
It's a feature™. You can set USE=-isohybrid if you want the vanilla .iso. Anyway, Portage does verify the original checksum for you, so I don't see why you would do that again.
ok, this is just an observation, this discrepancy may lead questions from users with increased security habits.