This is a confirmed error. We will get to it as soon as possible. If you can help to allocate time to it contact us.
I'll report here as soon as it is fixed
You can also support the project financially, a support contract or purchasing an incident resolution ticket would permit us to dedicate our programming resources directly to this issue instead of waiting for free time.
Omar fixed this on friday. I tested it yesterday and it seems to be working correctly now.
You can edit the report and select the correct grouping, once you save the graph will appear correctly on the home page.