Happy to report that after a little experimenting it seems that Gate A5 (with the current AFCAD I have) seems to be the only gate with the GSX2 issue. At all other gates (at least the ones I have tested) GSX2 functions as advertised. It seems that there must be a syntax error somewhere in the A5 AFCAD but as I have no idea how to correct this I have just made a note to avoid A5 on future departure/arrivals from/to OTHH.