That is a feature, not a bug.
In the patch notes it was clarified that only tier 4 and above tools (or magic) can harvest Starmetal.
Tier 1: Stone
Tier 2: Iron
Tier 3: Steel
Tier 4: Hardened Steel
This one has yet to see if a pickaxe counts a tier up from a pick of the same material, but will give a shot later, however, this is deliberate.
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