Class change with Property Calculator does not trigger Workflow

Hi, I have found a strange behavior when I change the class with Property Calculator and wanted to ask if anyone has the same problem.

I have set up an external source for one of our customers. It comes up with a PDF with xml. In the xml is a documenttype. I save this type in a value list and with Property Calculator I customize the class with this abbreviation. The assigned class (e.g. Invoice) has a forced workflow, but after the class change with Property Calculator there is no workflow.

If I change the class manually in the metadata card, it works fine and the workflow is there and in the first state.

Does anyone have the same problem and a solution for it?