ImageEditor -f pm1033o.png --project pm1033o.json 

Layer 3 has been physically deleted from the project, together with
any transform associated to it. There are 11 layers in the json, 
numbered: 1,2,4,5,6,7,8,9,10,11,12 (3 is missing).

When trying to create a new layer (you can use existing Polygon 11 or
create a new one or a lasso), this new layer will take the ID=12. There
will be 2 layers named 12. The new layer should be numbered MAX+1=13.
I suspect that it is set to NUM+1.

Note: Polygon 14 exists without 12 and 13.