1905 Hobart short paid postcard taxed twice

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I'm trying to work out why this card was taxed twice.

Card posted Jersey 29 DE 1904, hexagonal T / 15 / L (London) tax mark.

Card has writing on front, so treated as a letter. Postage paid 1d against required 2½d.

Hobart cds on front 9 FE 1905.

Double deficiency of 3d paid with 3d due pen cancelled.

A second 3d adhesive postmarked 11 FE 1905 over a purple DLO mark the applied (postmark ties the pen cancelled stamp).

What was the process for the second taxing?