Default [Q] Cellular data monthly usage showing wrong value

I'm trying to display the monthly data usage beginning with the 15th -> #NTMTHM15#
So now it should show the usage from the last 2 weeks, instead it shows only the last 24 hours.
Is it a bug in Zooper Widget or am I doing something wrong?

[Edit]
It actually shows the data usage for the current month (not the last 24hours as presumed)...