Karamba utilization vs von mises stress

Hi,

When calculating the utilization and the von mises stress of shell elements, I noticed something strange.

When multiplying the maximum utilization output with the material's yield strength, the maximum occuring von mises stress should be equal right?

But the value for the von mises stress is different (factor of about 0.9) (see picture).

Is there a factor included in the utilization calculation or do I have a different problem in the file?

Kind regards,

Stefan