Artboard Symbols being removed
create an artboard and select it and create a “Artboard Symbol” ... 
This creates the symbol but still keeps the artboard where it was but its name becomes purple so that it marks - it's a symbol kind of. Changes on this purple artboard will apply to the instances directly.

anyway, when I now select “remove unused” it will remove those artboards for some reason - that's not so cool because they are for sure “used” if they are lying on my stage.

please can you fix this? 
many thanks