PostgreSQL and Base - table design "read only"

I read that LibreOffice Base has a native Postgres driver, so I thought that might be a good way to play around with the database structure, creating new tables, altering and dropping existing ones etc.

Almost everything seems to work fine. I can connect to the DB and open and edit all tables, create new ones, delete existing ones. I can basically do everything, except change the data definition of existing columns (i.e., if I try to edit an existing table in the table design window, I can see the list of field names and field types but I cannot change any of them, all field properties are greyed out). So, I could delete the column entirely, and I can easily create new columns, or fields, in the same table. But once they’re there, I cannot change them anymore.

Could this be a bug or am I missing something else?