Delphi 1 TabbedNoteBook bug?

I just bump into a problem with the TabbedNoteBook:
(1) Create a new project with one MDI form and an MDI child.
(2) Put a panel as a toolbar on the MDI form and drop a button on the
(3) Put a tabbednotebook on the MDI child form, align client.
(4) Run the program and click the button on the main form.
(5) Now the tabs of the tabbednotebook will no longer work.

Any one know why it happens and any workaround?

BTW, it works fine under Delphi 3 but I have to code with the lowest common

Hardy Yau
Sierra Systems Consultants Inc