If you lose a planet the same turn you try to build a cactus, the build attempt will fail in Agave Tequilana. In Cactus2001, the cactus will be built and immediately be captured.
In Agave Tequilana, building a cactus always has precedence over voting "yes". In Cactus2001, it depends on the order in which commands are received.
Agave Tequilana tries to build cactuses in planet Id order, independant from the order of commands. Cactus2001 builds cactuses in the order it receives commands in.