Fieldsets can be configured so that they cannot be closed. The button for closing the fieldset is not rendered for this purpose. However, fieldsets can also be closed by clicking on the header. Initially, it looks as if this functionality is deactivated for non-collapsed fieldsets. However, the new value of the collapsed status is still entered in the personal configuration and thus read when the corresponding view is rendered again. This fieldset is then rendered closed.
Non-collapsible fieldsets must not listen to the click on the header to close.
== Test
Set a fieldset to non-collapsible, e.g. via the form editor. Click on the header of the fieldset in view mode, change the view and go back to the view with the fieldset so that the form is redrawn.