If you start a point map, select lat & lon fields, select a legend, and then run the visualisation, you get the legends you expect.
If you then change your mind about the legend and choose a different field, hitting Get Result reruns the query and redisplays the map, but the legend labels are still what you originally chose.
This is mystifying since the executed query has been correctly updated!
Reloading the whole page seems to fix it.