Two days of errors, finally got through to realise that the 'free seats' were only available one way and the outbound BKK-RGN flt was priced at USD150, making the short flight USD75 each way! Wasn't very impressed.

It was also annoying that, as someone mentioned earlier, the regular fares were accessed using the same interface, so the overload not only affected my search of free seats, but my search for regular seats outside sale times. Over the course of the sales these 'regular' seats went up significantly also.

It's tough being cheap :-)