[OBD U9.1] creating custom drawing seed without using existing drawing seed

Refering the to help page for "To Create a Custom Drawing Seed for a Section Callout", step 3:

https://docs.bentley.com/LiveContent/web/OpenBuildings%20Designer%20Help-v5.1.1/en/GUID-69C7925B-33E5-1647-CC51-AD9DC445F277.html

If you want to use the settings of an existing drawing seed, select it from the Drawing Seed drop-down list, else select (none).

If I leave the "drawing seed" field as "(none)", the "create drawing" checkbox is greyed out and unselectable. Is that a bug? 

Best regards,

Tuan Le