I used the bookmark to specify only one category (L3) to be displayed , save and when i return , i find always the 2 category not only the specified one (L3) please see (screeshot)
Usually, if you unselect collapsed All level member not only from the dropdown, but also from the dimension, leave only selected bookmarked member and save the report, only this selected bookmarked member should appear in the dropdown.
Tray again selecting All Categories member, expand and collapse it from the dropdown and, when collapsed, unselect from the dimension; save the report.