I have a DONE4 issued by CX with 6 dated segments and 10 open segments.

BA has a hard time dealing with this ticket. It is not accessible through "manage my booking." If I call BA they can find the PNR, but are unable to make seating choices on BA flights for dated segments (and I am BA Gold). Most agents just say the computer is down (since they are unable to pull up a seat map) and ask me to call back tomorrow. Other agents have speculated that it is because there are some open segments in the itinerary, but none have been successful getting me an upper deck seat on a BA flight.

Might have something to do with Amadeus - open segment issue noted above by CALCHAS? Anyone know a work-around to select a seat on a BA flight for a dated segment?