Burndown widget shows invalid data

Hi,

we are using RTC 3.0.1 usinf the CRUM template. We are running into problems using the Burndown widget. It does not show any valid data.
in the current sprint there are a couple of workitems. all of these workitems are estimated and have assigned a valid category. at least one
of those workitems are in state "in progress" but the burndown chart shows stupid data even if we run all data warehouse jobs manually.
if we click on the settings menu item of the burndown widget and then choose query we see 3 selection boxes. two out of the three are always empty (tem area
and iteration) but the third one has content. this box is called details.

does anyone have a solution to that issue ?

thanks and kind regards marco