Hi,
(Please use bottom-posting on this list).
I found two problems:
1. If I go to "Operations > Edit or export relational schema" and I
remove many tables from the page, then when I open the Designer, the
"Show/Hide left menu" displays all of the tables in the db with their
checkbox ticked, while these tables are (correctly) not displayed on the
work area.
2. Then, I click on "Save position" and "Open page" and I reopen the
same page: all tables of the db are now on the page.