Quite often on my system, also for others judging from the forums, signatures fail on pacman downloads:

error: perl: signature from "Florian Pritz <bluewind@xinu.at>" is invalid
error: failed to commit transaction (invalid or corrupted package (PGP signature))

The fix usually is to clear the pkg cache, -Syy and try again.

Is there a way this can be fixed on a lower level? I haven't seen this type of key sync issues on other signing distros (Debian in my case).