Classic Era, Anniversary servers.

This is the tooltip for a staff:
https://imgur.com/a/Cr6n24N

I tried both the in-build and the pawn scale and both with same result.

Try a spec override (not Pawn scale override) for arms warrior. Weapon validity is based on spec, and enhancement shaman is set to dual wield 1h weapons which is normally fine, but is only not ideal in this weird edge case.