Not sure how award IRROPs are handled by AB but in my experience with US/UA/AA irrops, the original plating carrier doesn't have to reissue because the operating carrier has control of the original coupon on day of departure.

What I think should have happened is this:
AB "lifts" the DUS-HAM coupon (submits to AA for reimbursement as if business as usual).
AB book LH DUS-HAM segment either in same PNR or new PNR and issues new ticket for this.

This is no different than putting me on ICE. AB is still going to submit the coupon to AA for reimbursement and DB is going to submit the train coupon back to AB for payment.

This is how I've seen this work in IRROPS between US, UA, and AA.

FYI According to the AA agent I spoke with while at the AB counter, they don't have an interline agreement with LH either (which I know to be untrue).