First off not all Star Alliance carriers use the same system. Amadeus is used by TG and LH but not by SQ or UA. If a reservation is made by one airline, it doesn;t always generate through to the other carriers. And remember just cause you can see your ticket, doesn;t mean that the agent on the phone can.

Saying that, Thai at LAX aren;t exactly the nicest or most efficient employees.

You might also want to know that unlike most STAR carriers, change fees will often be waived at TG offices for changes or reissues.
So its not all bad news.