AVE not AVO ;)) ... Alta Velocidad Española, or Spanish High Speed
It's weird though, can you give more details on the specific train? It might well be so, this operator has an inconsistent commercial policy sometimes. Also, try LOCO2.com It's notoriously known that Renfe's website is a piece of cr*p, unfriendly, full of bugs, etc. and it's quite a shame (for them!) that one -even when in Spain- sometimes gets a better service for some long distance purchases, for a similar price, on foreign webs such as Loco2, based in the UK or the SNCF in France.
On a sidenote: train operations in Spain, as in many countries in Europe, was state-run for many years, since its inception in the mid 1800s until fairly recent (late 20th century) In fact, there's talk at the EU Commission since 1991 about a complete liberalisation in all EU countries "soon". It is my experience that for the old state-run companies (RENFE is one) is very difficult to adapt to a culture of competition and while great progress is/can be made, there's always these 'dregs' especially regarding customer service. You wouldn't believe the information chaos when there's a break down! Now the market is semi-liberalised but so far no competitors have put forward a serious bid, probably because of the overwhelming size of RENFE. There are a few minor exceptions, such as FGC in Catalonia which operates since the late 1970s a sizable commuting network covering the inland routes around the metro area of Barcelona. Frankly, a delight in comparison!