Custom visual, matrix: Subtotals only received in packaged mode.

I'm developing a custom visual using matrix dataViewMappings.

My problem is that I only get the Subtotal values if I package the visual and import it,

and this way I can't rely on these data while running the visual in development mode.

The detailed bug report is here, but I start to think that it's a bug of a different tool and not powerbi-visuals-tools:

https://github.com/microsoft/PowerBI-visuals-tools/issues/288