I discovered it because I wanted to have the possibility to add items again when the default index page is activated. The possibility to add items is currently only available when the feature is deactivated. But as I read in the forum, this could be a feature in the next releases.
I guess this bug is in every filter function but just tested it in project management and policy exception.
You can reproduce it, when you
create a Filter and save it with “Show as default index page ? = YES”
reset the filter to default.