Hi emerich,
This is a known issue that appeared in ARCHICAD 20. The fix for it has already been released in ARCHICAD 21 (in the released version), and in the latest update of ARCHICAD 20 (build 7001). Please make sure that you have the latest version installed, and give it another go. If you are still experiencing the issue after the update, let us know, and send us your file as well.
Best of Luck,
Daniel Alexander Kovacs
Professional Services Consultant
GRAPHISOFT
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