I noticed it was possible to move zones within a layer or through different layers. You can find this as an obviousness, but it is not mentioned in the manual.
You just need to click-left for a while (1s) on the layer name and then drag and drop the zone. Short left-click is for renaming layers and zones.
This is very useful if you use subtractive layers, where zone order matters. And be aware also that moving a zone from a duplicated layer, means that we can also duplicate a zone.