i try to modify the page "packaging" of product, which is defined with groups="base.group_extended"

If the user is in this group all work very well.
If the user is not in this group, i have an error "list index out of range" when i just click on the menu. I think it's because the replace tag doesn't find the initial page.

I have the same problem by trying adding a new field after "variants", which is defined with the same "groups" tag. I make my after inheritance on another field and all works.

Is there a way to modify this page (or all other page with have a groups tag) ?